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Objective: This scoping review aimed to summarize current knowledge from twin studies on migraine. Migraine heritability, genetic correlations with migraine comorbid disorders, and the use of discordant twin pairs in migraine research are described. Further, the review considers the unused potential of twin studies in migraine research and reflects on future directions. Background: Twin studies can be used to understand how heritable and environmental factors influence human traits and disorders. The classical twin design compares the resemblance of a trait in monozygotic twins to that in dizygotic twins. The classical twin design can be extended to estimate the genetic correlation between disorders, model causality, and describe differences within discordant twin pairs. Methods: Studies focusing on migraine and using a twin study design were included. The search was performed on the PubMed‐MEDLINE database using the search terms "migraine" AND "twin" OR "twins." It was done in May 2023, rerun in November 2023, and managed with the Covidence software. Results: The search identified 52 twin studies on migraine. In 24 papers, the heritability of migraine was estimated with a classical twin design. Heritability estimates ranged from 0.36 to 0.48 for studies with adults, both men and women, and unspecified migraine. Migraine heritability was predominantly estimated with twin cohorts of North European ancestry, and only two studies examined migraine subtypes. A multilevel classical twin design was used in 11 studies to examine the co‐occurrence between migraine and comorbid disorders. The differences within migraine discordant twin pairs were examined in nine studies. Conclusion: The heritability of migraine was estimated with a classical twin design in twin cohorts from seven different countries, with remarkably similar results across studies. Future studies should include migraine subtypes and twin cohorts of non‐North European ancestry to better reflect the global population. Beyond heritability estimations, the twin method is a valuable tool for understanding causality and describing differences within discordant twin pairs. Despite more than 80 years of twin studies in migraine research, the twin design has a large unused potential to advance our understanding of migraine. Plain Language Summary: This review summarizes what has been learned about the inheritance of migraine from studies with twins. Studies with adults, both men and women, estimated the inheritance of migraine at about 36%–48%. However, most of these studies included twins with North European ancestry, and future studies should include twins from different parts of the world to understand how migraine affects people globally. [ABSTRACT FROM AUTHOR]

Background: The way in which socioeconomic status (SES) moderates the etiology of reading attainment has been explored many times, with past work often finding that genetic influences are suppressed under conditions of socioeconomic deprivation and more fully realized under conditions of socioeconomic advantage: a gene–SES interaction. Additionally, past work has pointed toward the presence of gene–location interactions, with the relative influence of genes and environment varying across geographic regions of the same country/state. Method: This study investigates the extent to which SES and geographical location interact to moderate the genetic and environmental components of reading attainment. Utilizing data from 2,135 twin pairs in Florida (mean age 13.82 years, range 10.71–17.77), the study operationalized reading attainment as reading comprehension scores from a statewide test and SES as household income. We applied a spatial twin analysis procedure to investigate how twin genetic and environmental estimates vary by geographic location. We then expanded this analysis to explore how the moderating role of SES on said genetic and environmental influences also varied by geographic location. Results: A gene–SES interaction was found, with heritability of reading being suppressed in lower‐ (23%) versus higher‐SES homes (78%). The magnitude of the moderating parameters were not consistent by location, however, and ranged from −0.10 to 0.10 for the moderating effect on genetic influences, and from −0.30 to 0.05 for the moderating effect on environmental influences. For smaller areas and those with less socioeconomic variability, the magnitude of the genetic moderating parameter was high, giving rise to more fully realized genetic influences on reading there. Conclusions: SES significantly influences reading variability. However, a child's home location matters in both the overall etiology and how strongly SES moderates said etiologies. These results point toward the presence of multiple significant environmental factors that simultaneously, and inseparably, influence the underlying etiology of reading attainment. [ABSTRACT FROM AUTHOR]

Objective: Reward‐based eating drives are putative mechanisms of uncontrolled eating implicated in obesity and disordered eating (e.g., binge eating). Uncovering the genetic and environmental contributions to reward‐related eating, and their genetic correlation with BMI, could shed light on key mechanisms underlying eating and weight‐related disorders. Method: We conducted a classical twin study to examine how much variance in uncontrolled eating phenotypes and body mass index (BMI) was explained by genetic factors, and the extent that these phenotypes shared common genetic factors. 353 monozygotic twins and 128 dizygotic twins completed the Reward‐based Eating Drive 13 scale, which measures three distinct uncontrolled eating phenotypes (loss of control over eating, preoccupation with thoughts about food, and lack of satiety), and a demographic questionnaire which included height and weight for BMI calculation. We estimated additive genetic (A), common environmental (C), and unique environmental (E) factors for each phenotype, as well as their genetic correlations, with a multivariate ACE model. A common pathway model also estimated whether genetic variance in the uncontrolled eating phenotypes was better explained by a common latent uncontrolled eating factor. Results: There were moderate genetic correlations between uncontrolled eating phenotypes and BMI (.26–.41). Variance from the uncontrolled eating phenotypes was also best explained by a common latent uncontrolled eating factor that was explained by additive genetic factors (52%). Discussion: These results suggest that uncontrolled eating phenotypes are heritable traits that also share genetic variance with BMI. This has implications for understanding the cognitive mechanisms that underpin obesity and disordered eating. Public Significance: Our study clarifies the degree to which uncontrolled eating phenotypes and BMI are influenced by shared genetics and shows that vulnerability to uncontrolled eating traits is impacted by common genetic factors. [ABSTRACT FROM AUTHOR]

Background: Stress is a universal phenomenon and one of the most common precipitants of insomnia. However, not everyone develops insomnia after experiencing a stressful life event. This study aims to test aspects of Spielman's '3P model of insomnia' (during adolescence) by exploring the extent to which: (a) insomnia symptoms are predicted by polygenic scores (PGS); (b) life events predict insomnia symptoms; (c) the interaction between PGS and life events contribute to the prediction of insomnia symptoms; (d) gene–environment interaction effects remain after controlling for sex. Methods: The sample comprised 4,629 twins aged 16 from the Twin Early Development Study who reported on their insomnia symptoms and life events. PGS for insomnia were calculated. In order to test the main hypothesis of this study (a significant interaction between PGS and negative life events), we fitted a series of mixed effect regressions. Results: The best fit was provided by the model including sex, PGS for insomnia, negative life events, and their interactions (AIC = 26,158.7). Our results show that the association between insomnia symptoms and negative life events is stronger for those with a higher genetic risk for insomnia. Conclusions: This work sheds light on the complex relationship between genetic and environmental factors implicated for insomnia. This study has tested for the first time the interaction between genetic predisposition (PGS) for insomnia and environmental stressors (negative life events) in adolescents. This work represents a direct test of components of Spielman's 3P model for insomnia which is supported by our results. [ABSTRACT FROM AUTHOR]

Background: The association of sleep bruxism with mortality has not been studied. Objectives: Altogether 12 040 subjects from the nationwide Finnish twin cohort were included in the analyses. We examined whether self‐reported sleep bruxism is associated with increased risk of mortality, and if so, whether the effect is independent of known common risk factors. The time span of the follow‐up was 30 years. Methods: Cox proportional hazards regression models (Hazard Ratios and their 95% Confidence Intervals) adjusted by age, sex and covariates were used to assess the effect of baseline bruxism status in 1990 on future mortality in 1990–2020. Results: The risk of mortality among all participants (n = 12 040), independent of missing covariates and adjusted by age and sex, was 40% higher in weekly bruxers than in never bruxers (HR 1.40, 95% CI 1.16–1.68, p <.001). However, when adjusted by all studied covariates, (n = 11 427) the risk was no longer observed (HR 1.04, 95% CI 0.86–1.25, p =.717). Despite the overall lack of between bruxism and mortality after adjustment for covariates, we examined the cause‐specific risks for major cause‐of‐death groups. There were no substantial associations of weekly bruxism with major disease outcomes by the fully adjusted hazard ratios for them. Conclusion: Bruxism does not kill—in line with its definition of being rather a behaviour (with all its phenotypes) than a disease. [ABSTRACT FROM AUTHOR]

Background: Due to different assessment modes employed, a clear picture of the prevalence of sleep bruxism across time cannot be formed. Moreover, studies on the persistent or fluctuating nature of sleep bruxism have yielded divergent and even contradictory results. The aim of the present study was to evaluate in a nationwide twin cohort whether self‐reported sleep bruxism was correlated longitudinally, pairwise and cross‐twin over a 20‐year period. Objectives: Self‐reported bruxism was assessed in 1990 and 2011 by mailed questionnaires in the Finnish Twin Cohort study of same‐sex twins born 1945–1957. Methods: We assessed the phenotypic stability over time for all participating individuals (n = 4992). Among zygosity verified pairs (n = 516 MZ and n = 837 DZ), we estimated the cross‐sectional zygosity correlations and the zygosity‐specific cross‐twin cross‐time correlations. Results: Reported bruxism appeared rather persistent over time without significant difference regarding zygosity. The overall phenotypic longitudinal correlation was 0.540 and somewhat higher in men (0.596) than in women (0.507). Pairwise trait correlations in 1990 and 2011 were higher in MZ than in DZ pairs. The cross‐twin cross‐time correlations were higher in MZ twins than in DZ twins, but less than the cross‐sectional MZ and DZ pairwise correlations. Conclusions: The higher correlation of reported sleep bruxism in the cross‐twin cross‐time analyses in MZ than in DZ pairs implies a genetic background for bruxism persistence. Also, bruxism over time in individual twins appears to be fairly persistent and somewhat higher in men than women. [ABSTRACT FROM AUTHOR]

Objective: To compare the maternal and neonatal outcomes of twin pregnancies between vertex and nonvertex presentations of the second twin in vaginal delivery. Methods: In this unicentric retrospective cohort study, we collected data from 213 cases of vaginal twin deliveries from January 2016 to July 2020. Participants were divided into the vertex‐vertex presentation group (VV) and vertex‐breech presentation group (VB). Data on maternal and neonatal outcomes were compared between groups. Results: Among the 213 mothers and 426 infants (213 twin pairs), there were 140 women in the VV group and 73 women in the VB group (65.73% vs. 34.27%). Infants in the VB group had a higher incidence of admission to NICU (51.43% vs. 68.49%, p = 0.017), lower 1‐min (11.43% vs. 28.77%, p < 0.001) and 5‐minute Apgar scores (1.43% vs. 4.11%, p = 0.043) for the second twin. However, after the adjustment for sex of the twin, birth weight, chorionicity, and gestational age, the greater risk of admission to NICU and low 5‐min Apgar score was no longer significantly different. Conclusion: VB twins are at no greater overall risk of a poor outcome due to breech presentation in the second twin. However, the presentation of the second fetus represents a risk factor for a low 1‐min Apgar score. Obstetricians and midwives should consider appropriate interventions for second twins who present breech versus vertex. [ABSTRACT FROM AUTHOR]

Background: Attention‐deficit/hyperactivity disorder (ADHD) is an increasingly commonly diagnosed neurodevelopmental condition. One possibility is that this reflects a genuine increase in the prevalence of ADHD due to secular environmental changes, yet this hypothesis remains untested. We therefore investigated whether the genetic and environmental variance underlying ADHD, and traits of ADHD, has changed over time. Methods: We identified twins born from 1982 to 2008 from the Swedish Twin Registry (STR). We linked the STR with the Swedish National Patient Register and Prescribed Drug Register to identify diagnoses of ADHD and prescriptions of ADHD medication for these twins. We also utilized data collected from participants in the Child and Adolescent Twin Study in Sweden (CATSS), born from 1992 to 2008. Their parents completed a structured ADHD screening tool, which was used to measure traits of ADHD and assign broad screening diagnoses of ADHD. We used the classical twin design to test whether the degree to which variation in these measures was influenced by genetic and environmental variation changed over time. Results: We included 22,678 twin pairs from the STR and 15,036 pairs from CATSS. The heritability of ADHD in the STR ranged from 66% to 86% over time, although these fluctuations were not statistically significant. We observed a modest increase in variance in ADHD traits, from 0.98 to 1.09. This was driven by small increases in the underlying genetic and environmental variance, with heritability estimated as 64%–65%. No statistically significant changes in variance in screening diagnoses were observed. Conclusions: The relative contribution of genetic and environmental factors to ADHD has remained stable over time, despite its increasing prevalence. Thus, changes in the underlying etiology of ADHD over time are unlikely to explain the increase in ADHD diagnoses. [ABSTRACT FROM AUTHOR]

Background: Twin studies have demonstrated shared genetic and environmental effects between eating disorders and alcohol involvement in adults and middle adolescents. However, fewer studies have focused on late adolescents or investigated a wide range of eating disorder dimensions and alcohol involvement subscales in both sexes. We examined genetic and environmental correlations among three eating disorder dimensions and two alcohol involvement subscale scores in late adolescent twins using bivariate twin models. Methods: Participants were 3568 female and 2526 male same‐sex twins aged 18 years old from the Child and Adolescent Twin Study in Sweden. The Eating Disorder Inventory‐2 (EDI) assessed the drive for thinness, bulimia, and body dissatisfaction. Alcohol involvement was assessed with the Alcohol Use Disorder Identification Test consumption (AUDIT‐C) and problem (AUDIT‐P) subscales. Results: Only phenotypic and twin correlations in female twins met our threshold for twin modeling. The proportion of total variance for each trait accounted for by additive genetic factors ranged from 0.50 to 0.64 in female twins, with the rest explained by nonshared environmental factors and measurement error. Shared environmental factors played a minimal role in the variance of each trait. The strongest genetic correlation (ra) emerged between EDI bulimia and AUDIT‐P (ra = 0.46, 95% confidence interval: 0.37, 0.55), indicating that the proportion of genetic variance of one trait that was shared with the other trait was 0.21. Nonshared environmental correlations between eating disorder dimensions and alcohol involvement ranged from 0.03 to 0.13. Conclusions: We observed distinct patterns of genetic and environmental effects for co‐occurring eating disorder dimensions and alcohol involvement in female vs. male twins, supporting sex‐specific treatment strategies for late adolescents with comorbid eating disorders and alcohol use disorder. Our findings emphasize the importance of assessing family history of multiple eating disorder dimensions while treating late adolescents with problematic alcohol use, and vice versa, to improve detection and treatment. [ABSTRACT FROM AUTHOR]

Summary: Background: Being born with intrauterine growth restriction (IUGR) was associated with subsequent health issues later in life. However, the underlying role of adipokines in IUGR is unknown. Objectives: To measure the adiponectin and leptin concentrations in the cord blood of monochorionic (MC) twins with selective IUGR (sIUGR) and evaluate their associations with childhood growth trajectories. Methods: Cord blood samples were collected from 22 pairs of MC twins with sIUGR and 20 pairs of normal MC twins. Adiponectin and leptin concentrations in cord blood were determined by ELISA. Data regarding perinatal outcomes and infantile growth trajectories from birth to 24 months were obtained. Results: Only cord blood adiponectin concentrations were associated with IUGR (β −1.51, 95% CI −2.45, −0.57, p = 0.002), and cord blood leptin concentrations were significantly lower in sIUGR twins compared to normal twins (2.8 ± 1.6 vs. 6.4 ± 3.0, p < 0.001). Adiponectin concentrations were negatively associated with height increments from birth to 6 months (β −0.28, 95% CI −0.51, −0.06, p = 0.015). Leptin concentrations were negatively associated with weight at 6 and 24 months (β −0.12 95% CI −0.22, −0.02, p = 0.002; β −0.18 95% CI −0.33, −0.03, p = 0.019) and weight and height increments from birth to 6 months (β −0.17 95% CI −0.29, −0.06, p = 0.020; β −0.40 95% CI −0.81, −0.01, p = 0.037). Conclusion: Cord blood adiponectin concentrations were negatively associated with IUGR but did not predict childhood growth. Cord blood leptin concentrations were inversely associated with weight and height increments in the first 6 months. [ABSTRACT FROM AUTHOR]

Background: Individual differences in symptoms of behaviour problems in childhood and adolescence are not primarily due to nature or nurture – another substantial source of variance is non‐shared environment (NSE). However, few specific environmental factors have been found to account for these NSE estimates. This creates a 'missing NSE' gap analogous to the 'missing heritability' gap, which refers to the shortfall in identifying DNA differences responsible for heritability. We assessed the extent to which variance in behaviour problem symptoms during the first two decades of life can be accounted for by measured NSE effects after controlling for genetics and shared environment. Methods: The sample included 4,039 pairs of twins in the Twins Early Development Study whose environments and symptoms of behaviour problems were assessed in preschool, childhood, adolescence and early adulthood via parent, teacher and self‐reports. Twin‐specific environments were assessed via parent‐reports, including early life adversity, parental feelings, parental discipline and classroom environment. Multivariate longitudinal twin model‐fitting was employed to estimate the variance in behaviour problem symptoms at each age that could be predicted by environmental measures at the previous age. Results: On average across childhood, adolescence and adulthood, parent‐rated NSE composite measures accounted for 3.4% of the reliable NSE variance (1.0% of the total variance) in parent‐rated, symptoms of behaviour problems, 0.5% (0.1%) in teacher‐rated symptoms and 0.9% (0.5%) in self‐rated symptoms after controlling for genetics, shared environment and error of measurement. Cumulatively across development, our parent‐rated NSE measures in preschool, childhood and adolescence predicted 4.7% of the NSE variance (2.0% of the total variance) in parent‐rated and 0.3% (0.2%) in self‐rated behaviour problem symptoms in adulthood. Conclusions: The missing NSE gap between variance explained by measured environments and total NSE variance is large. Home and classroom environments are more likely to influence behaviour problem symptoms via genetics than via NSE. [ABSTRACT FROM AUTHOR]

Background: From birth, infants orient preferentially to faces, and when looking at the face, they attend primarily to eyes and mouth. These areas convey different types of information, and earlier research suggests that genetic factors influence the preference for one or the other in young children. Methods: In a sample of 535 5‐month‐old infant twins, we assessed eye (relative to mouth) preference in early infancy, i.e., before neural systems for social communication and language are fully developed. We investigated the contribution of genetic and environmental factors to the preference for looking at eyes, and the association with concurrent traits and follow‐up measures. Results: Eye preference was independent from all other concurrent traits measured, and had a moderate‐to‐high contribution from genetic influences (A = 0.57; 95% CI: 0.45, 0.66). Preference for eyes at 5 months was associated with higher parent ratings of receptive vocabulary at 14 months. No statistically significant association with later autistic traits was found. Preference for eyes was strikingly stable across different stimulus types (e.g., dynamic vs. still), suggesting that infants' preference at this age does not reflect sensitivity to low‐level visual cues. Conclusions: These results suggest that individual differences in infants' preferential looking to eyes versus mouth to a substantial degree reflect genetic variation. The findings provide new leads on both the perceptual basis and the developmental consequences of these attentional biases. [ABSTRACT FROM AUTHOR]

Background and Aims: Previous studies have demonstrated associations between substance use and reduced educational attainment; however, many were unable to account for potential confounding factors like genetics and the rearing environment. In the few studies that controlled for these factors, the substances assessed were limited to alcohol, cannabis, and tobacco. To address these limitations, we examined the relationship between adolescent use of seven kinds of substances, the number of additional substances used, and high school noncompletion within a large sample of Australian twins. Design: A series of two‐level generalized mixed effects logistic regressions were conducted to examine associations between adolescent substance use and high school noncompletion. Setting: Australia. Participants: A total of 9579 adult Australian twins from two cohorts of the Australian Twin Registry. Measurements Assessments of high school completion, childhood major depression, conduct disorder symptoms, substance use initiation, demographics, and parental educational attainment using the Australian version of the Semi‐Structured Assessment for the Genetics of Alcoholism. Findings There were unique within‐twin‐pair effects of use of sedatives (odds ratio [OR] = 22.39 [95% confidence interval (CI) = 1.18–423.48]) and inhalants/solvents (OR = 10.46 [95% CI = 1.30–84.16]) on high school noncompletion. The number of substances used in adolescence was strongly associated with high school noncompletion across all discordant twin models (ORs from 1.50–2.32, Ps < 0.03). Conclusions: In Australia, adolescent substance use appears to be associated with early school dropout, with the effects of any given substance largely because of the confounding factors of parental education, childhood conduct disorder symptoms, and use of other substances. Sedatives and inhalants/solvents have effects on high school noncompletion that cannot be explained by polysubstance use or familial factors. [ABSTRACT FROM AUTHOR]

The objective of this paper is to describe gestational weight gain (GWG), to assess the applicability of the 2009 Institute of Medicine (IOM) guidelines, and to derive a GWG adequacy classification within a French cohort. We included twins from the national, prospective, population‐based JUmeaux MODe d'Accouchement (JUMODA) cohort study (2014–2015). Following the IOM approach, we selected a 'standard' population of term pregnancies with 'optimal' birthweight (≥2500 g; n = 2562). GWG adequacy (insufficient; adequate; excessive) was defined using IOM recommendations (normal body mass index [BMI]: 16.8–24.5 kg [also utilized for underweight BMI]; overweight: 14.1–22.7 kg; obese: 11.4–19.1 kg). Additionally, using the IOM approach, we determined the 25th and 75th percentiles of GWG in our standard population to create a JUMODA‐derived GWG adequacy classification. GWG and GWG adequacy were described, overall and by BMI and parity. In the JUMODA standard population of term twin livebirths with optimal birthweight, mean GWG was 16.1 kg (standard deviation 6.3). Using IOM recommendations, almost half (46.5%) of the women had insufficient and few (10.0%) had excessive GWG, with similar results regardless of BMI or parity. The 25th and 75th percentiles of GWG in the JUMODA standard population (underweight: 13–21 kg; normal weight: 13–20 kg; overweight: 11–19 kg; obese: 7–16 kg) were lower than the IOM recommendations. The IOM recommendations classified a relatively high percentage of French women as having insufficient and a low percentage as having excessive GWG. Additional research to evaluate recommendations in relation to adverse perinatal outcomes is needed to determine whether the IOM recommendations or the JUMODA‐derived classification is more appropriate for French twin gestations. Key messages: Using the 2009 Institute of Medicine (IOM) recommendations to define gestational weight gain (GWG) adequacy in our French cohort classified almost half of women as having insufficient GWG and a relatively low percentage as having excessive GWG.The USA‐derived IOM definition for adequate GWG may not apply in France or in other non‐USA, contemporary obstetric populations.Additional research in large, population‐based contemporary cohorts with prospective GWG ascertainment and assessment of GWG adequacy classifications in relation to adverse outcomes is needed to inform evidence‐based GWG recommendations for twin pregnancies. [ABSTRACT FROM AUTHOR]

Background: COVID‐19 was associated with significant financial hardship and increased binge eating (BE). However, it is largely unknown whether financial stressors contributed to BE during the pandemic. We used a longitudinal, cotwin control design that controls for genetic/environmental confounds by comparing twins in the same family to examine whether financial hardship during COVID‐19 was associated with BE. Methods: Female twins (N = 158; Mage = 22.13) from the Michigan State University Twin Registry rated financial stressors (e.g., inability to afford necessities) daily for 49 consecutive days during COVID‐19. We first examined whether financial hardship was associated with BE phenotypes across the full sample. We then examined whether cotwins who differed on financial hardship also differed in BE. Results: Participants who experienced greater mean financial hardship across the study had significantly greater dimensional BE symptoms, and participants who experienced greater financial hardship on a given day reported significantly more emotional eating that day. These results were replicated in cotwin control analyses. Twins who experienced more financial hardship than their cotwin across the study reported greater dimensional BE symptoms than their cotwin, and participants who experienced more financial hardship than their cotwin on a given day reported greater emotional eating that day. Results were identical when restricting analyses to monozygotic twins, suggesting associations were not due to genetic confounds. Conclusions: Results suggest that BE‐related symptoms may be elevated in women who experienced financial hardship during COVID‐19 independent of potential genetic/environmental confounds. However, additional research in larger samples is needed. Public Significance: Little is known regarding how financial difficulties during the COVID‐19 pandemic may have contributed to increased binge eating (BE). We found preliminary evidence that financial hardship during COVID‐19 may be associated with greater rates of BE‐related symptoms even when comparing twins from the same family. While additional research is needed, results suggest that people who experienced financial hardship during COVID‐19 may be at increased risk for BE. [ABSTRACT FROM AUTHOR]

Background: Chaotic home environments may contribute to children's attention‐deficit hyperactivity disorder (ADHD) symptoms. However, ADHD genetic risk may also influence household chaos. This study investigated whether children in chaotic households had more ADHD symptoms, if mothers and children with higher ADHD genetic risk lived in more chaotic households, and the joint association of genetic risk and household chaos on the longitudinal course of ADHD symptoms across childhood. Methods: Participants were mothers and children from the Environmental Risk (E‐Risk) Longitudinal Twin Study, a UK population‐representative birth cohort of 2,232 twins. Children's ADHD symptoms were assessed at ages 5, 7, 10 and 12 years. Household chaos was rated by research workers at ages 7, 10 and 12, and by mother's and twin's self‐report at age 12. Genome‐wide ADHD polygenic risk scores (PRS) were calculated for mothers (n = 880) and twins (n = 1,999); of these, n = 871 mothers and n = 1,925 children had information on children's ADHD and household chaos. Results: Children in more chaotic households had higher ADHD symptoms. Mothers and children with higher ADHD PRS lived in more chaotic households. Children's ADHD PRS was associated with household chaos over and above mother's PRS, suggesting evocative gene–environment correlation. Children in more chaotic households had higher baseline ADHD symptoms and a slower rate of decline in symptoms. However, sensitivity analyses estimated that gene–environment correlation accounted for a large proportion of the association of household chaos on ADHD symptoms. Conclusions: Children's ADHD genetic risk was independently associated with higher levels of household chaos, emphasising the active role of children in shaping their home environment. Our findings suggest that household chaos partly reflects children's genetic risk for ADHD, calling into question whether household chaos directly influences children's core ADHD symptoms. Our findings highlight the importance of considering parent and child genetic risk in relation to apparent environmental exposures. [ABSTRACT FROM AUTHOR]

Aims: The extent to which maternal transmission of primary dysmenorrhoea is genetically determined in adolescents and young women has yet to be determined. We aimed to assess heritability and associations relevant to primary pain syndromes using a twin family study. Methods: Participants were young menstruating female twins, and their oldest sisters and mothers, whose families were registered with Twins Research Australia and previously participated in a twin family study of primary paediatric pain disorders. Questionnaire packs were mailed, assessing current maximum and average menstrual pain intensity, current pain interference with activities and retrospective dysmenorrhea secondary symptoms. Results: The sample comprised 206 twin individuals (57 monozygous (MZ) and 46 dizygous (DZ) pairs) aged 10–22 years, eldest siblings (n = 38) aged 13–28 years and mothers (n = 101) aged 32–61 years. The estimated regression coefficient of the relationship between mother–daughter and twin–sibling dyads indicated significant associations for the measures of dysmenorrhea and supported heritability. Adjusted for age, the within twin‐pair correlation for MZ twins was generally more than twice that of DZ twins. Heritability estimates were maximal pain intensity 0.67 (P = 3.8 × 10−11), average pain intensity 0.63 (P = 3.7 × 10−10), pain interference 0.57 (P = 1.8 × 10−8) and retrospective symptoms 0.57 (P = 1.8 × 10−8). Twin individuals with a lifetime (three‐month) history of iron deficiency and those with painless restless legs syndrome (RLS) were significantly more likely to have more intense pain associated with menstruation. Conclusion: Primary dysmenorrhea in adolescents and young women was shown to be relatively strongly genetically influenced and associated especially with a history of iron deficiency and painless RLS which have potential therapeutic implications. [ABSTRACT FROM AUTHOR]

Background: We sought to clarify the impact of adolescent alcohol misuse on adult physical health and subjective well‐being. To do so, we investigated both the direct associations between adolescent alcohol misuse and early midlife physical health and life satisfaction and the indirect effects on these outcomes attributable to subsequent alcohol problems. Method: The sample included 2733 twin pairs (32% monozygotic; 52% female) from the FinnTwin16 study. Adolescent alcohol misuse was a composite of frequency of drunkenness, frequency of alcohol use, and alcohol problems at ages 16, 17, and 18.5. The early midlife outcomes included somatic symptoms, self‐rated health, and life satisfaction at age 34. The mediators examined as part of the indirect effect analyses included alcohol problems from the Rutgers Alcohol Problem Index at ages 24 and 34. Serial mediation and co‐twin comparison models were applied and included covariates from adolescence and early midlife. Results: There were weak direct associations between adolescent alcohol misuse and early midlife physical health and life satisfaction. However, there was stronger evidence for indirect effects, whereby young adult and early midlife alcohol problems serially mediated the relationship between adolescent alcohol misuse and early midlife somatic symptoms (β = 0.03, 95% CI [0.03, 0.04]), self‐rated health (β = −0.02, 95% CI [−0.03, −0.01]), and life satisfaction (β = −0.03, CI [−0.04, −0.02]). These serial mediation effects were robust in co‐twin comparison analyses. Conclusions: These results provide evidence that alcohol problems are a primary driver linking adolescent alcohol misuse and poor health outcomes across the lifespan. [ABSTRACT FROM AUTHOR]

Objective: This study aimed to report the prevalence of adverse psychological symptoms and health behaviours of parents who had a baby admitted to a regional neonatal intensive care unit to spotlight mental health care in these unique settings. Design: This was a prospective, prevalence‐based study using quantitative data. Setting: The study was conducted at the Townsville University Hospital, Queensland. Participants: Participants comprised 114 parents of 79 infants enrolled in the study (mothers = 69 and fathers = 45). Main outcome measures: Trauma, depression, anxiety, stress, alcohol and drug use, prior mental health history and bonding experience were assessed by standardised self‐report questionnaires and a structured diagnostic interview within 2 weeks and at 3 months post‐admission to neonatal intensive care unit. Results: Clinically significant acute trauma symptoms (16% of mothers only), depression (22% mothers; 4% of fathers), anxiety (27% mothers; 11% fathers) and stress (24% mothers; 13% fathers) were reported within the first 2 weeks after their baby was admitted to the neonatal intensive care unit. Notably, 18% of parents reported engaging in harmful alcohol use behaviour within 2 weeks post‐birth; 29% of fathers continued to report risky drinking at 3 months. At 3 months, 21%, 8% and 6% of mothers met diagnostic criteria for generalised anxiety disorder, major depressive disorder and post‐traumatic stress disorder, respectively. Conclusion: Screening for psychological distress and alcohol use of parents of neonatal intensive care unit babies can ensure that support services are made available post‐discharge to optimise family function and development of the preterm infant. [ABSTRACT FROM AUTHOR]

Background: Difficulties initiating and maintaining sleep (DIMS) are frequent features of autism, yet little is known about why these conditions co‐occur. One possibility is that they share etiological factors, yet this hypothesis remains to be tested using quantitative genetic designs. We thus investigated etiological links between autism and DIMS using familial co‐aggregation and twin methods. Methods: Twins, siblings, half‐siblings, and cousins of 50,097 individuals with autism were identified from Swedish population registries. Their risk of DIMS, defined through diagnoses of insomnia and/or melatonin prescriptions, was then estimated. Twin analyses conducted on 15,279 child and adolescent twin pairs investigated etiological links between DIMS and ASD. Results: 22.8% of autistic individuals had DIMS. Monozygotic co‐twins of individuals with autism were most at risk of DIMS compared to the reference group (OR = 6.6 [2.5–17.4]), followed by dizygotic co‐twins (OR = 2.6 [1.5–4.5]) and full siblings (OR = 2.5 [2.4–2.6]). Half‐siblings and cousins of individuals with autism were least likely to have DIMS relative to the reference group (OR range = 1.3–1.5). Twin analyses estimated a correlation of 0.57 (0.53–0.61) between autism and DIMS, with a genetic correlation of 0.62 (0.60–0.68). These overlapping genetic factors explained 94% of the covariance between these conditions. Autistic traits also showed genetic overlap with DIMS. Conclusions: Our results suggest that shared genetic mechanisms underlie autism and DIMS, which may lead them to co‐occur. Untangling the etiological overlap between these conditions has potential to assist in understanding the etiology of each condition, as well as their associated outcomes. [ABSTRACT FROM AUTHOR]

Background: Shame is considered a maladaptive self‐conscious emotion that commonly co‐occurs alongside depression and anxiety. Little is known, however, about the aetiology of shame and its associations with depression and anxiety. We estimated, for the first time, genetic and environmental influences on shame and on its associations with depression and anxiety in adolescence. Methods: The sample was twin and sibling pairs from the Genesis 1219 Study (Time 1, N = 2,685; males 42.8%, Mage = 14.95, SD = 1.67, age range: 12–21; Time 2, N = 1618; males 39.7%, Mage = 16.97, SD = 1.64, age range: 14–23). Participants completed validated questionnaires to measure shame (at Time 1), depression and anxiety (at Times 1 and 2). Results: Shame was moderately to strongly associated with concurrent depression and anxiety. Prospectively, shame was significantly associated with an increase in depression, but not anxiety. Genetic analyses revealed that shame was moderately heritable with substantial nonshared environmental influence. The associations between shame and concurrent depression and anxiety were primarily accounted for by overlapping genetic influences. Prospectively, the association between shame and later depression was primarily accounted for by genetic and nonshared environmental influences shared with earlier depression. The unique association between shame and later depression was mostly explained by common nonshared environmental influences. Conclusions: The findings offer novel evidence regarding aetiology of shame—although moderately heritable, shame in adolescents may also result from nonshared environmental factors. Genetic and nonshared environmental influences contribute to the co‐occurrence of shame with depression and anxiety. [ABSTRACT FROM AUTHOR]

Objective: To explore the current practice and perceptions of health visitors in supporting multiple birth families. Design and sample: Practicing health visitors across the United Kingdom were invited to complete a cross‐sectional, descriptive, online survey. The questionnaire covered multiple birth caseload, education received about multiples and the experience of working with families. Two‐hundred and ninety health visitors completed the questionnaire. Descriptive and inferential statistics were used for analysis of the quantitative components and thematic analysis for the qualitative data. Results: Most health visitors had twins on their current workload. Most health visitors had not received any specific training or continuing professional development regarding the needs of multiple birth families. Supporting the families within the confines of reduced time and increased workload was challenging. Daily tasks of caring for multiples were the main areas that health visitors and parents wanted more information about. Conclusions: In the United Kingdom, health visitors are uniquely positioned to support multiple birth families, in particular during the more challenging early years. However, the findings of this study suggest that many health visitors are aware that the care and support that they are able to provide multiple birth families falls short of meeting their needs [ABSTRACT FROM AUTHOR]

Background: Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder with a strong genetic basis. Recent studies have suggested that its aetiology is also influenced by environmental factors. Some of the most examined environmental factors are obstetric complications. However, the results are inconsistent. Methods: We aimed to explore the association between obstetric complications and autism in a population‐based twin sample using the Obstetric Enquiry Scale (OES), a scale that measures the presence or absence of pre‐, peri‐ and neonatal factors. Additionally, we report the meta‐analytic results for obstetrical factors reported in previously published sibling studies. Results: Our study included 115 cases pairs and 62 controls pairs and showed that children with autism and their unaffected co‐twins present significantly more obstetric complications than controls (ASD vs. controls β 1.26, CI 95% 1.11–1.40 p <.001; unaffected co‐twin vs. controls β 1.20, 95% CI 1.07–1.36 p <.003). However, we did not find statistically significant differences between children with ASD and their unaffected co‐twins (β.96, 95% CI 0.85–1.09, p 0.55). Meta‐analysis demonstrated that maternal hypertension (RR 1.35, CI 95% 1.23–1.48), uterine bleeding (RR 1.20 CI 95% 1.01–1.42) and exposure to antibiotic during pregnancy (1.11 CI 95% 1.00–1.22) increase risk of ASD. Conclusions: This study confirms that children with ASD and their unaffected twins show more obstetric complications than controls. However, these complications do not distinguish between ASD twins and their unaffected co‐twins. In addition, the meta‐analysis showed little influence of birth factors on ASD which suggests a shared familial liability for both obstetric complications and autism, rather than a causal association. [ABSTRACT FROM AUTHOR]

Introduction: Our study compared the prospective risks of intrauterine fetal death (IUFD), neonatal death (NND), perinatal death (PND), and neonatal morbidities in monochorionic diamniotic (MCDA) and dichorionic diamniotic (DCDA) twin pregnancies. Methods: This retrospective cohort study included twin pregnancies who had antenatal care and delivery in a public hospital from 2011 to 2018. Exclusion criteria included monoamnionicity, one/both twin miscarriage, twin‐twin transfusion syndrome, or lethal congenital abnormalities. All twins were managed in multiple pregnancy clinic with standardized protocols. Gestational age‐specific IUFD, NND, PND, and neonatal morbidity rates were compared according to chorionicity. Results: Three hundred seventy‐eight MCDA and 1282 DCDA twins were included. MCDA twins had higher risks of PND (1.9% vs. 0.7% in DCDA twins, p = 0.05), composite neonatal morbidity (p = 0.01), preterm delivery (p < 0.01), and low birth weight (p < 0.01). The prospective risk of IUFD was 0.6% and 0.4% for MCDA and DCDA twins, respectively after 34 weeks' gestation. No NND occurred among deliveries after 30 weeks. The risk of neonatal morbidity of MCDA twins fell from 22.7% at 34 weeks to 2.7% at 37 weeks (p < 0.01). For DCDA twins, the risk of morbidity fell insignificantly from 36 to 38 weeks (4.0% vs. 3.4%, p = 0.60). Logistic regression analysis suggested that the increased risk of perinatal morbidities was related to the higher rate of preterm delivery in MCDA twins rather than chorionicity. Conclusion: With close fetal monitoring, the risk of late IUFD in twin pregnancies without major complications is low. Perinatal morbidity can be minimized by avoiding late preterm deliveries in twin pregnancies. [ABSTRACT FROM AUTHOR]

Background: Research has demonstrated that individuals who identify as a sexual minority (e.g., gay/lesbian, bisexual) are at increased risk for suicidality‐related outcomes. However, previous research is primarily limited by the lack of adjustment for unmeasured (i.e., genetic and environmental) confounding factors and previous psychopathology. Methods: Using the Child and Adolescent Twin Study in Sweden, we employed a co‐twin control design to examine the extent to which the association between sexual orientation and adolescent suicide attempt and self‐harm (SA/SH) was independent of genetic and environmental factors shared by twins, as well as measured symptoms of childhood psychopathology. Results: Adolescents who identified as a sexual minority (i.e., gay/lesbian, bisexual, or other sexual orientation) were at two‐fold increased odds for SA/SH (OR, 2.01 [95% confidence interval, 1.63–2.49) compared to heterosexual adolescents. When adjusting for all genetic and shared environmental factors that make twins similar and for measured childhood psychopathology, the association remained positive but attenuated to OR, 1.55 (1.11–2.16). Conclusions: Identifying as a sexual minority was associated with approximately 50% increased odds of SA/SH in adolescence after adjusting for unmeasured genetic and environmental factors shared by twins and for childhood psychopathology. The results support that environmental factors specifically associated with identifying as a sexual minority likely increase risk for SA/SH. Our findings highlight the need to monitor suicidality risk among this group. [ABSTRACT FROM AUTHOR]

Aims: To identify drug use typologies based on substances used and persistence of use over two time points, use a genetically informed design to explore twin concordance of and genetic influence on the use typologies and compare patterns of declined/discontinued ("desistant") and persistent drug use on drug use correlates. Design Latent class analysis was applied to data from a cross‐sectional self‐report survey on current and past drug use. Use characteristics, use disorder, and psychiatric problems were compared across classes. Setting: Computer‐assisted telephone interview in respondents' homes. Participants: A total of 3785 individual twins and siblings (1365 men, 2420 women; Mage = 32) from the Australian Twin Registry Cohort III. Measurements A comprehensive interview assessed prior to past year and past year use of cannabis, stimulants, cocaine/crack, hallucinogens, opioids, sedatives, inhalants, dissociatives, and solvents; age of first use; opportunity to use; peer drug use; attention deficit/hyperactivity, conduct, antisocial personality, depressive, and substance use disorders; and suicidality. Findings A five‐class solution emerged: no/low use (50%), desistant cannabis use (23%), desistant party drug use (18%), persistent prescription drug misuse (4%), and persistent polydrug use (5%). Twin concordances were higher among monozygotic (k = 0.30–0.35) than dizygotic pairs (same‐sex k = 0.19–0.20; opposite sex k = 0.07), and biometric modeling suggested that the persistent polydrug use class, in particular, was highly heritable (a2 = 0.94). Conduct disorder (OR = 2.40), antisocial personality disorder (OR = 3.27), and suicidal ideation (OR = 1.98) increased persistent polydrug use risk; depression (OR = 2.38) and lifetime suicide attempt (OR = 2.31) increased persistent prescription misuse risk. Relative to persistent prescription drug misuse, persistent polydrug use was associated with higher rates of cannabis and stimulant use disorder (OR = 6.14–28.01), younger first substance use (OR = 0.82–0.83), more drug use opportunity (OR = 10.66–66.06), and more drug‐using peers (OR = 4.66–9.20). Conclusions: Unique patterns of declined/discontinued ("desistant") and persistent drug use are differentially heritable and differentially associated with risk factors, psychiatric symptoms, and substance use disorder outcomes. [ABSTRACT FROM AUTHOR]

Aims: To investigate whether the Institute of Medicine (IOM) guidelines for optimal gestational weight gain (GWG) in twin pregnancies are applicable to Japanese women. Methods: This was a retrospective study involving women who delivered full‐term twins at our tertiary center diagnosed with a normal prepregnancy body mass index. The women were divided into two groups, according to the optimal GWG recommended by the IOM (16.8–24.5 kg): the adequate GWG (AGWG) group with GWG meeting the guidelines and the low GWG (LGWG) group with GWG below the guidelines. Next, the women were divided into two groups according to birthweight: a group with both twins born appropriate for gestational age (AGA group) and a group with one or both twins born small for gestational age (SGA group). Their GWG as well as their pregnancy outcomes were compared. Results: A total of 265 women were included. The AGWG group had a significantly higher proportion of hypertensive disorders of pregnancy than the LGWG group. There was no significant difference in the proportion of women with both twins born AGA or the rate of admission to the neonatal intensive care unit. Meanwhile, the median GWG in the AGA group was 13.6 kg, which was significantly higher than 12.0 kg in the SGA group. And even the median GWG in the AGA group was below the lower limit of the IOM guidelines. Conclusion: The optimal GWG for Japanese women with twin pregnancies may be below the IOM guidelines. [ABSTRACT FROM AUTHOR]

Background: Top‐down volitional command of eye movements may serve as a candidate endophenotype of ADHD, an important function underlying goal‐directed action in everyday life. In this twin study, we examined the relation between performance on a response inhibition eye‐tracking paradigm and parent‐rated ADHD traits in a population‐based twin sample. We hypothesized that altered eye movement control is associated with the severity of ADHD traits and that this association is attributable to genetic factors. Methods: A total of 640 twins (320 pairs, 50% monozygotic) aged 9–14 years) from the Child and Adolescent Twin Study in Sweden (CATSS) participated. Twins performed the antisaccade task indexing inhibitory alterations as either direction errors (following exogenous cues rather than instructions) or premature anticipatory eye movements (failure to wait for cues). We calculated the associations of eye movement control and ADHD traits using linear regression mixed‐effects models and genetic and environmental influences with multivariate twin models. Results: Premature anticipatory eye movements were positively associated with inattentive traits (β =.17; 95% CI: 0.04, 0.31), while controlling for hyperactive behaviors and other covariates. Both premature anticipatory eye movements and inattention were heritable (h2 = 0.40, 95% CI: 0.22, 0.56; h2 = 0.55; 95% CI: 0.42, 0.65; respectively), and their genetic correlation was small but statistically significant (r =.19, 95% CI: 0.02, 0.36). However, the genetic correlation did not remain significant after adjusting for covariates (age, sex, hyperactivity traits, IQ). No link was found between direction errors and ADHD traits. Conclusions: This study indicates that there is a specific, genetically influenced, relation between top‐down eye movement control and the inattentive traits typical of ADHD. [ABSTRACT FROM AUTHOR]

Background: Evidence suggests that the trend toward early planned births observed among singletons may be evident among twin pregnancies. Aims: To describe trends in gestational age at birth, pregnancy characteristics, neonatal morbidity and mortality among twin pregnancies. Materials and Methods: Population‐based data linkage study of twin births of ≥30 weeks of gestation without a major congenital anomaly born in 2003–2014 in New South Wales (NSW), Australia. Linked pregnancy and birth, hospital and mortality data were used. Generalised linear regression was used to assess linear trends. Risk difference (RD) and 95% confidence intervals were estimated. Results: Among 28 076 eligible twin births (14 038 pregnancies), 49% of births occurred prior to 37 weeks and 69% of births were planned (pre‐labour caesarean or induction of labour). There were increases over time in the proportion of twin births at preterm gestations (30–34 weeks (RD 2.1, 95% CI 0.1, 4.0), 35–36 weeks (RD 7.5, 95% CI 5.4, 9.7)) and in the rates of planned births (pre‐labour caesarean (RD 6.4, 95% CI 4.0, 8.8), induction (RD 4.6, 95% CI 2.6, 6.6)). There was no significant change in stillbirth or neonatal death rates, but there was an increase in neonatal morbidity over the study period. Concurrently, there were increases in the prevalence of gestational diabetes; and decreases in pregnancy hypertension, assisted reproductive technology use, small‐for‐gestational age and birthweight discordance. Conclusions: Gestational age at birth among twin births is decreasing and birth intervention is increasing. There are increasing rates of neonatal morbidity, but no overall change in perinatal mortality. [ABSTRACT FROM AUTHOR]

Motives for physical activity may vary considerably by age, sex, and the level of physical activity. We aimed to examine motives for physical activity in older men and women with different physical activity levels as well as whether genetic and/or environmental factors explain those motives. Finnish twins (mean age 72.9 years, 262 full twin pairs) self‐reported their motives for physical activity. Time spent on moderate‐to‐vigorous physical activity was monitored using a hip‐worn accelerometer. Comparisons between the different physical activity groups of older twins (n = 764‐791/motive dimension) were analyzed using the Wald test, and effect sizes were calculated as Cohen's d. Quantitative genetic modeling was used to estimate genetic and environmental contributions. For both sexes, the most frequently reported motives for physical activity were physical fitness, health maintenance, and psychological well‐being. Conforming to others' expectations was more important for men than for women (P <.001, Cohen's d = 0.38), while appearance (P =.001 Cohen's d = −0.24) and psychological well‐being (P =.02, Cohen's d = −0.17) were highlighted by women. Most of the motive dimensions differed significantly between the physically active and inactive individuals. It was estimated that 5%‐42% of the variation in motives was contributed by genetic factors and 58%‐95% by environmental factors. The result that environmental factors contribute in a great deal to motives indicates that interventions to motivate physically inactive older individuals to be physically active can be successful. However, personalized interventions are needed because sex and the level of physical activity were found to be associated with older individuals' motives for physical activity. [ABSTRACT FROM AUTHOR]

Aim: To compare the outcome of intracytoplasmic sperm injection (ICSI) pregnancies complicated by spontaneous loss of a dichorionic co‐twin with that of singleton ICSI pregnancies. Methods: The study group included dichorionic ICSI pregnancies with co‐twin loss (n = 33) and the control group included ICSI pregnancies with a singleton from the beginning (n = 327). Primary outcome measures were obstetric complications, including preterm delivery, newborn small for gestational age, gestational diabetes, gestational hypertensive disorders and abruptio placenta; admission to neonatal intensive care unit (NICU) and perinatal mortality observed in the study and control groups. Statistical analysis was performed using spss for Windows, version 22.0. Results: In the study group, there were 26 cases of first trimester (early) and 7 cases of second or third trimester (late) co‐twin losses. Mean gestational age at delivery and mean birth weight were significantly lower in the whole study group compared to control (P < 0.05). Preterm delivery and NICU admission rates were significantly higher in the whole study group, compared to control (39.3% vs 14.6% and 36.36% vs 11.69% respectively, P < 0.05), but did not show significant difference between early loss subgroup and control (P > 0.05). Preterm delivery rate was significantly higher in the late loss subgroup compared to the early loss subgroup (85.71% vs 26.92% P < 0.05). Conclusion: Loss of a co‐twin in dichorionic ICSI pregnancies is associated with increased risk of preterm birth. This risk is significantly higher in cases with late loss compared to the early loss cases. [ABSTRACT FROM AUTHOR]

Background: Many adult drinkers consume far beyond the binge threshold. This "high‐intensity drinking" (HID), defined as 2 (HID‐2) and 3 (HID‐3) times the binge threshold, is of public health interest due to its role in acute alcohol‐related harms. Research on HID has mostly been limited to college‐aged young adults, focused on contextual factors, and neglected the potential role of genetic influences on the propensity to engage in HID. Methods: Structured diagnostic interviews assessing past‐year alcohol involvement were conducted with 3,785 individuals (1,365 men, 2,420 women; Mage = 32, range = 21 to 46), including 3,314 twins and 471 nontwin siblings from the Australian Twin Registry. Multinomial logistic regression analyses were conducted to compare HID‐2 and HID‐3 to binge drinking on demographic correlates, drinking characteristics, and drinking‐related consequences. Biometric modeling was conducted to estimate the role of genetic, common, and individual‐specific environmental factors in HID propensity. Results: Among past‐year drinkers, the prevalence of HID‐2 and HID‐3 was both 22%, with men disproportionally represented. The frequencies of drinking, intoxication, and binge drinking significantly increased across the heavier drinking categories, which also evidenced higher average consumption quantities and higher rates of alcohol‐related consequences. The propensity to engage in HID was significantly heritable (A = 37% [95% CI: 28 to 46%]), with individual‐specific environmental influences accounting for the remainder of the variance. Conclusions: This study convincingly demonstrates that HID is not restricted to college‐aged young adults, but also can be highly prevalent among those of working age, and that the propensity to engage in HID is partially explained by genetic influences. [ABSTRACT FROM AUTHOR]

Background: The number of vaginal breech and twin deliveries may be insufficient for adequate training. Objective: To determine whether advanced trainees and new Fellows in obstetrics are gaining adequate experience and confidence in vaginal breech and twin deliveries. Methods: An online survey was emailed to registered Royal Australia and New Zealand College of Obstetrics and Gynaecology (RANZCOG) advanced trainees and new Fellows (Years 1–5). This survey asked about their experience, confidence and whether they intend to perform vaginal breech and twin deliveries as specialists. Results: The survey was sent to 703 advanced trainees (162) and Fellows (541) and answered by 217 (31.7%). Experience and confidence in vaginal breech and twin deliveries increased with the number of procedures performed (P < 0.001) in both groups and were significantly higher among Fellows. Despite the level of experience, 100% of respondents felt confident in managing vaginal twin deliveries with or without supervision, whereas 14.9% of respondents did not feel confident in managing vaginal breech deliveries. Intention to offer these procedures in their practice depended on confidence levels, and there was a significant difference between twins and breech. Overall, 87.3% of respondents intended to offer vaginal twin deliveries in their practice, while only 32.7% intended to offer vaginal breech deliveries. Conclusion: Confidence in complex vaginal deliveries increases with increasing number of procedures performed and a significant proportion of trainees and Fellows consider they do not have sufficient experience. The association between confidence and intention to offer these procedures is stronger in twins than in breech deliveries. [ABSTRACT FROM AUTHOR]

Objective: To examine the association between inter‐twin delivery interval and short‐term perinatal outcomes of the second twin after vaginal delivery of the first twin. Methods: Retrospective cohort study including twin pregnancies with a vaginal delivery of the first twin between January 2011 and September 2017 in a tertiary hospital in Melbourne, Australia. The main outcome measure was a composite of adverse neonatal outcome (at least one of perinatal death, admission to neonatal intensive care unit (NICU), endotracheal intubation, Apgar <7 at five minutes and cord lactate >4.0 mmol/L). Proportions of adverse outcomes for the second twin were compared between groups of intervals ≤ or >10 and ≤ or >30 min. Results: The composite adverse neonatal outcome occurred in 201 (58.2%) and a caesarean section occurred in seven cases (2%) of the 345 pregnancies included. Delivery interval was associated with higher cord lactate. Low Apgar scores were more frequent with intervals >30 min (17.9% vs 6.6%, P = 0.03), as well as caesarean section for the second twin (10.7% vs 1.3%, P = 0.01). Composite adverse outcome and admission to NICU were not significantly influenced by the delivery interval. Predictors of adverse outcome were gestational age, abnormal cardiotocography and breech delivery of the second twin. Conclusion: The inter‐twin delivery interval is associated with higher rates of low Apgar scores and higher cord lactate for the second twin. These associations do not translate into higher rates of admission to NICU and their long‐term clinical implications are uncertain. [ABSTRACT FROM AUTHOR]

Background: The birthweight of multiples is naturally lower than that of singletons. Given that the incidence of twin pregnancy has risen in recent years, it seems reasonable to create standards of birthweight separately for twins. This could help in the objective assessment of small and large for gestational age twin newborns. The main goal of this study was therefore to construct and present up‐to‐date birthweight references. Methods: The present percentile charts for twins are based on a cohort retrospective study of 757 pairs of twins (767 boys and 709 girls) born between weeks 25 and 39 of gestation. Mean and standard deviation were calculated for the subsequent weeks of gestation. Percentiles were read for the subsequent gestational age. The obtained curves were smoothed with a fifth‐degree polynomial function. The significance of differences between the 50th percentile values for twins and singletons was estimated using median test. Results: In both sexes, a continuous observable trend occurs of a significantly lower average birthweight for twins. Differences increase with increasing gestational age and are greater in girls. The estimated 50th percentile for twins was greater than the estimated 10th percentile for singletons. This supports the notion of discordant growth as a physiological adaptation that promotes maturity. Conclusions: Percentile charts for singletons are not applicable for twins. This indicates the importance of applying separate percentile charts for twins, enabling objective evaluation of their health status and identifying deviations from normality. [ABSTRACT FROM AUTHOR]

Background and Aims The DSM-IV personality disorders (PDs) are comorbid with alcohol use disorder (AUD) and with each other. It remains unclear which PD criteria are most likely to drive onset and recurrence of AUD and which are merely confounded with those criteria. We determine which individual PD criteria predict AUD and the degree of underlying genetic and/or environmental aetiology. Design A prospective observational twin study. Setting Norway 1999-2011. Participants A total of 2528 and 2275 Norwegian adult twins in waves 1 and 2 variable-selection analyses, and 2785 in biometric analyses. Measurements DSM-IV PDs and their 80 criteria were assessed using a structured personal interview, and AUD using the World Health Organization's Composite International Diagnostic Interview. Findings In a variable-selection analysis, two PD criteria were associated with AUD even after taking all the other criteria into account: criterion 8 of antisocial PD (childhood conduct disorder) and criterion 4 of borderline PD (self-damaging impulsive behaviours). Adjusting for each other, their respective odds ratios were 3.4 [confidence interval (CI) = 2.1-5.4] and 5.0 (CI = 3.3-7.7). Endorsement strength of the criteria was associated with AUD in a dose-response manner and they explained 5.5% of variation in AUD risk-more than the full diagnoses of antisocial and borderline PDs together (0.5%). The association between borderline criterion 4 and AUD 10 years later derived mainly from their overlapping genetic factors, whereas the association between antisocial criterion 8 and AUD 10 years later was due to both genetic and non-genetic factors. Conclusions Conduct disorder and self-harming impulsivity are the foremost risk traits for alcohol use disorder among the 80 personality disorder criteria of DSM-IV, predicting alcohol use disorder more effectively than personality disorder diagnoses. The twin-study analysis suggested that conduct disorder represents a joint genetic and developmental risk for alcohol use disorder and that impulsivity is a genetic risk. [ABSTRACT FROM AUTHOR]

Purpose:The benefits of physical activity (PA) in preventing abdominal obesity are well recognized, but the role of different sport disciplines remains open. We aimed, therefore, to investigate how participation in different sport disciplines, and the number and types of sports engaged in are associated with waist circumference (WC) in young adulthood.Methods:This population-based cohort study comprised 4027 Finnish twin individuals (1874 men), with a mean age of 34 y (32–37), who answered a survey, including self-measured WC. We extracted the number and identified the types (aerobic, power, and mixed) of the different sport disciplines respondents reported participating in.Results:The number of sport disciplines participated in was inversely associated with WC, the linear decrease averaging 1.38 cm (95% CI 1.10–1.65) per each additional sport discipline. The result persisted after adjustment for the main covariates, such as volume of PA and diet quality. Among dizygotic twin pairs discordant for sports participation (0–2 vs. 5 or more disciplines), the mean within-pair difference in WC was 4.8 cm (95% CI 0.4–9.1) for men and 11.2 cm (95% CI 4.4–18.0) for women; among discordant monozygotic pairs, no differences were observed. In men, all three types of sports were individually associated with smaller WC, while in women, only mixed and power sports showed this association.Conclusions:Participation in several sport disciplines and sport types was associated with smaller WC among young adults in their mid-30s. Shared genetic background may explain some of the associations. [ABSTRACT FROM PUBLISHER]

Objective: Recent data show significant phenotypic and genetic associations between ovarian hormones and binge eating in adulthood. Theories of hormonal risk focus on puberty and the possibility that hormone activation induces changes in genetic effects that then lead to differential risk for binge eating in postpuberty and adulthood. Although this theory is difficult to test in humans, an indirect test is to examine whether genetic influences on binge eating increase during the pubertal period in girls. Prior work has shown pubertal increases in genetic influences on overall disordered eating symptoms, but no study to date has examined binge eating. The present study was the first to examine these increases for binge eating. Methods: Participants included 1,568 female twins (aged 8-25 years) from the Michigan State University Twin Registry. Binge eating and pubertal development were assessed with self-report questionnaires. Results: Twin moderation models showed significant linear increases in genetic effects from prepuberty (5%) to postpuberty (42%), even after controlling for the effects of age and body mass index. Discussion: Results provide critical support for increased genetic influences on binge eating during puberty. Additional studies are needed to identify hormonal mechanisms and fully test contemporary models of ovarian hormone risk. [ABSTRACT FROM AUTHOR]

There is limited empirical information as to whether or how stimuli associated with dental fear can be classified into distinct subtypes. The purpose of the current study was to develop a descriptive framework for the classification of dental fear. Data were collected using a survey among Dutch twin families ( n = 11,771). The sample was randomly divided into two subsamples of, respectively, 5,920 and 5,851 individuals. An exploratory factor analysis ( EFA) was performed on the first subsample to delineate the multidimensional structure of a set of 28 dental-fear-provoking objects and situations. The second sample was used to confirm the newly derived model using confirmatory factor analysis ( CFA). The EFA yielded a three-factor solution with 70.7% explained variance pertaining to: (i) invasive treatment or pain; (ii) losing control; and (iii) physical sensations. The CFA showed an acceptable fit to the data, thereby confirming the stability of the three-factor structure. There are at least three different subtypes of dental fear. As these subtypes require a different treatment approach in clinical practice, it could be important to assess the severity of patients' fear response along these three dimensions. [ABSTRACT FROM AUTHOR]

Background Childhood behavior problems predict subsequent educational achievement; however, little research has examined the etiology of these links using a longitudinal twin design. Moreover, it is unknown whether genetic and environmental innovations provide incremental prediction for educational achievement from childhood to adolescence. Methods We examined genetic and environmental influences on parental ratings of behavior problems across childhood (age 4) and adolescence (ages 12 and 16) as predictors of educational achievement at age 16 using a longitudinal classical twin design. Results Shared-environmental influences on anxiety, conduct problems, and peer problems at age 4 predicted educational achievement at age 16. Genetic influences on the externalizing behaviors of conduct problems and hyperactivity at age 4 predicted educational achievement at age 16. Moreover, novel genetic and (to a lesser extent) nonshared-environmental influences acting on conduct problems and hyperactivity emerged at ages 12 and 16, adding to the genetic prediction from age 4. Conclusions These findings demonstrate that genetic and shared-environmental factors underpinning behavior problems in early childhood predict educational achievement in midadolescence. These findings are consistent with the notion that early-childhood behavior problems reflect the initiation of a life-course persistent trajectory with concomitant implications for social attainment. However, we also find evidence that genetic and nonshared-environment innovations acting on behavior problems have implications for subsequent educational achievement, consistent with recent work arguing that adolescence represents a sensitive period for socioaffective development. [ABSTRACT FROM AUTHOR]

Background: 'Food fussiness' (FF) is the tendency to be highly selective about which foods one is willing to eat, and emerges in early childhood; 'food neophobia' (FN) is a closely related characteristic but specifically refers to rejection of unfamiliar food. These behaviors are associated, but the extent to which their etiological architecture overlaps is unknown. The objective of this study was to quantify the relative contribution of genetic and environmental influences to variation in FF and FN in early childhood; and to establish the extent to which they share common genetic and environmental influences. Method: Participants were 1,921 families with 16-month-old twins from the Gemini birth cohort. Parents completed the Child Eating Behaviour Questionnaire which included three FF items and four FN items. Bivariate quantitative genetic modeling was used to quantify: (a) genetic and environmental contributions to variation in FF and FN; and (b) the extent to which genetic or environmental influences on FF and FN are shared across the traits. Results: Food fussiness and FN were strongly correlated (r = .72, p < .001). Proportions of variation in FF were equally explained by genetic (.46; 95% CI: 0.41-0.52) and shared environmental influences (.46; 95% CI: 0.41-0.51). Shared environmental effects accounted for a significantly lower proportion of variation in FN (.22; 95% CI: 0.14-0.30), but genetic influences were not significantly different from those on FF (.58, 95% CI: 0.50-0.67). FF and FN largely shared a common etiology, indicated by high genetic (.73; 95% CI: 0.67-0.78) and shared environmental correlations (.78; 95% CI: 0.69-0.86) across the two traits. Conclusions: Food fussiness and FN both show considerable heritability at 16 months but shared environmental factors, for example the home environment, influenced more interindividual differences in the expression of FF than in FN. FF and FN largely share a common etiology. [ABSTRACT FROM AUTHOR]

Background: Developmental dyslexia (DD) and attention deficit/hyperactivity disorder (ADHD) are among the most common neurodevelopmental disorders, whose etiology involves multiple risk factors. DD and ADHD co-occur in the same individuals much more often than would be expected by chance. Several studies have found significant bivariate heritability, and specific genes associated with either DD or ADHD have been investigated for association in the other disorder. Moreover, there are likely to be gene-by-gene and gene-by-environment interaction effects (G × G and G × E, respectively) underlying the comorbidity between DD and ADHD. We investigated the pleiotropic effects of 19 SNPs spanning five DD genes (DYX1C1, DCDC2, KIAA0319, ROBO1, and GRIN2B) and seven DD environmental factors (smoke, miscarriage, birth weight, breastfeeding, parental age, socioeconomic status, and parental education) for main, either (a) genetic or (b) environmental, (c) G × G, and (d) G × E upon inattention and hyperactivity/ impulsivity. We then attempted replication of these findings in an independent twin cohort. Methods: Marker-trait association was analyzed by implementing the Quantitative Transmission Disequilibrium Test (QTDT). Environmental associations were tested by partial correlations. G × G were investigated by a general linear model equation and a family-based association test. G × E were analyzed through a general test for G × E in sib pair-based association analysis of quantitative traits. Results: DCDC2-rs793862 was associated with hyperactivity/impulsivity via G × G (KIAA0319) and G × E (miscarriage). Smoke was significantly correlated with hyperactivity/impulsivity. We replicated the DCDC2 × KIAA0319 interaction upon hyperactivity/impulsivity in the twin cohort. Conclusions: DD genetic (DCDC2) and environmental factors (smoke and miscarriage) underlie ADHD traits supporting a potential pleiotropic effect. [ABSTRACT FROM AUTHOR]

Background: Low self-worth during adolescence predicts a range of emotional and behavioural problems. As such, identifying potential sources of influence on self-worth is important. Aspects of the parent-child relationship are often associated with adolescent self-worth but to date it is unclear whether such associations may be attributable to familial confounding (e.g. genetic relatedness). We set out to clarify the nature of relationships between parental expressed affection and adolescent self-worth, and parent-child closeness and adolescent self-worth. Methods: We used data from the Twin and Offspring Study in Sweden, a children-of-twins sample comprising 909 adult twin pairs with adolescent children. Using these data we were able to apply structural equation models with which we could examine whether associations remained after accounting for genetic transmission. Results: Results demonstrated that parent-child closeness and parental-expressed affection were both phenotypically associated with adolescent self-worth. Associations could not be attributed to genetic relatedness between parent and child. Conclusions: Parent-child closeness and parental affection are associated with adolescent self-worth above and beyond effects attributable to genetic relatedness. Data were cross-sectional, so the direction of effects cannot be confirmed but findings support the notion that positive parent-child relationships increase adolescent self-worth. [ABSTRACT FROM AUTHOR]

Background Resilience has been shown to be protective against alcohol use disorders (AUDs), but the magnitude and nature of the relationship between these 2 phenotypes are not clear. The aim of this study was to examine the strength of this relationship and the degree to which it results from common genetic or common environmental influences. Methods Resilience was assessed on a 9-point scale during a personal interview in 1,653,721 Swedish men aged 17 to 25 years. AUD was identified based on Swedish medical, legal, and pharmacy registries. The magnitude of the relationship between resilience and AUD was examined using logistic regression. The extent to which the relationship arises from common genetic or common environmental factors was examined using a bivariate Cholesky decomposition model. Results The 5 single items that comprised the resilience assessment (social maturity, interest, psychological energy, home environment, and emotional control) all reduced risk for subsequent AUD, with social maturity showing the strongest effect. The linear effect by logistic regression showed that a 1-point increase on the resilience scale was associated with a 29% decrease in odds of AUD. The Cholesky decomposition model demonstrated that the resilience-AUD relationship was largely attributable to overlapping genetic and shared environmental factors (57 and 36%, respectively). Conclusions Resilience is strongly associated with a reduction in risk for AUD. This relationship appears to be the result of overlapping genetic and shared environmental influences that impact resilience and risk of AUD, rather than a directly causal relationship. [ABSTRACT FROM AUTHOR]

Aim To evaluate the incidence of twin-twin transfusion syndrome (TTTS) and the perinatal outcome at 28 days of age in monochorionic diamniotic (MCDA) pregnancies complicated with isolated polyhydramnios (I-Poly) and isolated oligohydramnios (I-Oligo) diagnosed < 26 weeks of gestation. Methods This was a retrospective study of women with MCDA pregnancies diagnosed with I-Poly or I-Oligo before 26 weeks of gestation over a period of six years. The incidence of subsequent TTTS and neonatal outcome in terms of intact survival (IS) at 28 days of age were evaluated. Intact survival was defined as being alive without any neurological complications at 28 days of age. Results There were 30 cases of I-Poly and 53 of I-Oligo that were eligible as per the inclusion criteria. Subsequent TTTS were complicated in six (20.0%) of the I-Poly and 26 (49.0%) of the I-Oligo cases. Among subjects with I-Poly, 17 had spontaneously normalized amniotic fluid volume. Prolonged oligohydramnios until intrauterine death, delivery or the onset of emerging TTTS was noted in 16 cases of I-Oligo. Both the twins exhibited IS in 26 (86.7%) cases of I-Poly and 31 (58.4%) cases of I-Oligo. Conclusion One-fifth of I-Poly and half of I-Oligo MCDA twins at < 26 weeks of gestation potentially develop TTTS. I-Oligo in particular should be regarded as a high-risk condition as neonatal IS is less than 60%. [ABSTRACT FROM AUTHOR]

Objective The Twin Birth Study, an international, multi-center randomized controlled trial was conducted to compare the risks of planned cesarean with planned vaginal delivery for twin pregnancies. The aim of this component of the trial was to understand participants' perspectives of study participation and preferences for the mode of delivery. Methods A mixed-methods questionnaire was distributed to study participants 3 months after giving birth. The questionnaire contained Likert scales and open-ended questions about the experience of being enrolled in a clinical trial and of childbirth, including the mode of delivery. Quantitative data were analyzed using SAS to generate descriptive statistics. Qualitative data were analyzed to identify categories and themes. Results Ninety-one percent of trial participants completed the questionnaire. Across all groups, the majority of women would participate in a study like this one again if given the opportunity. Main benefits of participating were as follows: benefits to one and one's babies, altruism, and receiving quality care. Randomization for the mode of delivery was challenging for women because of the desire to be involved in decision-making. Findings related to childbirth experience and the mode of delivery demonstrated a preference for vaginal birth across all groups. Those who had a vaginal birth were more satisfied with their birth experience. Conclusions This study provides evidence to inform practitioners about what women who have twin pregnancies like or dislike about birth and their desire for involvement in decision-making. Vaginal birth was preferred across all study groups and was associated with greater satisfaction with childbirth experience. [ABSTRACT FROM AUTHOR]

ABSTRACT Objective To examine the occurrence, course, and clinical picture of the DSM-5 residual categories 'Other Specified Feeding or Eating Disorder' (OSFED) and 'Unspecified Feeding or Eating Disorder' (UFED), to describe potential subtypes, and to evaluate whether the subdivision of the residual category appears meaningful. Method We screened women from the 1975-79 birth cohorts of Finnish twins ( N = 2825) for lifetime eating disorders using questionnaires and the SCID interview. This analysis characterizes women who reported clinically significant eating disorder symptoms but did not fulfill diagnostic criteria for DSM-5 anorexia nervosa (AN), bulimia nervosa (BN), or binge eating disorder (BED). Results Thirty-eight women (21% of those with an eating disorder) fell in the residual OSFED/UFED category. A third of them ( N = 14) fulfilled OSFED criteria, whereas two thirds ( N = 24) fell in the UFED category. The lifetime prevalence of OSFED/UFED was 1.5% (95% CI 1.1-2.0%), less than half of the prevalence of DSM-IV eating disorder not otherwise specified (EDNOS). The mean age of onset of OSFED/UFED was 18 years, median duration of symptoms was two years, and the 5-year probability of recovery was 60%. Over a third of women with OSFED/UFED suffered from comorbid psychiatric disorders. Both residual categories were clinically heterogeneous and included atypical forms of AN, BN, and BED. Conclusions Applying the DSM-5 criteria in a community sample of young women more than halved the occurrence of residual eating disorder diagnoses, but resulted in two instead of one clinically heterogeneous residual categories. Nevertheless, residual eating disorders were associated with considerable clinical severity. © 2016 Wiley Periodicals, Inc. (Int J Eat Disord 2016; 49:1010-1017) [ABSTRACT FROM AUTHOR]

Objective Gestational hypertensive disease ( GHD) is associated with pregnancy-related complications and poor maternal and fetal outcomes in singleton pregnancies. We sought to examine the influence of GHD in a large prospective cohort of twin pregnancies. Study design The ESPRIT study was a national multicenter observational cohort study of 1028 structurally normal twin pregnancies. Each pregnancy underwent sonographic surveillance with two-week ultrasound from 24 weeks for dichorionic and from 16 weeks for monochorionic gestations. Characteristics and demographics as well as labour and delivery outcome data were prospectively recorded. Perinatal mortality, admission to the neonatal intensive care unit (NICU) and a composite of morbidity of respiratory distress syndrome, hypoxic ischaemic encephalopathy, periventricular leukomalacia, necrotising enterocolitis and sepsis were documented for all cases. Outcomes for patients with documented GHD (pre-eclampsia and gestational hypertension) were compared with those without GHD. Results Perinatal outcome data were recorded for 977 patients. Women with GHD had a higher body mass index (27.1 ± 6.4 vs 25.2 ± 4.5, P < 0.0001) than those without and were more likely to be nulliparous (65% (59/92) vs 46% (407/885), P = 0.001). Both groups had similar mean birthweights, but those with GHD were more likely to have a birthweight discordance ≥18% (35% (32/92) vs 20% (179/885), P = 0.001). Rates of caesarean delivery were higher in those twin pregnancies affected by GHD, and while the rate of composite morbidity was similar in both groups, twins in the GHD group had higher rates of NICU admission. Conclusion In twin gestations, gestational hypertension independently confers an increased risk for emergency caesarean delivery, birthweight discordance and NICU admission, such that intensive maternal-fetal monitoring is justified when hypertension develops in a twin pregnancy. [ABSTRACT FROM AUTHOR]

In the self-worth model, burnout is considered to be a syndrome of performance-based self-esteem (PBSE) and experiences of exhaustion. Studies have shown that PBSE and burnout indices such as Pines' Burnout Measure (BM) are associated. Whether these variables have overlapping etiologies has however not been studied before. Genetic and environmental components of covariation between PBSE and exhaustion measured with Pines' BM were examined in a bivariate Cholesky model using data from 14,875 monozygotic and dizygotic Swedish twins. Fifty-two per cent of the phenotypic correlation (r = 0.41) between PBSE and Pines' BM was explained by genetics and 48% by environmental factors. The findings of the present study strengthen the assumption that PBSE should be considered in the burnout process as proposed by the self-worth conception of burnout. The present results extend our understanding of the link between this contingent self-esteem construct and exhaustion and provide additional information about the underlying mechanisms in terms of genetics and environment. This finding corroborates the assumed syndrome view on burnout, while it also suggests an altered view of how the syndrome emerges and how it can be alleviated. [ABSTRACT FROM AUTHOR]

Aims To develop a model based on clinical and ultrasound parameters to predict the risk of cesarean delivery after labor induction in near-term twin gestations. Methods This retrospective cohort study included 189 consecutive women with twin gestations at ≥ 36.0 weeks scheduled for labor induction. The Bishop score and transvaginal ultrasonographic measurements of cervical length were obtained immediately before labor induction. Parameters studied included maternal age, height, weight, parity, gestational age, Bishop score, cervical length, epidural analgesia, method of conception, chorionicity and birth weight. Prostaglandin E2 (dinoprostone) and oxytocin were used for labor induction. Logistic regression analysis and receiver operating characteristic curve were used to generate a predictive model for cesarean delivery. Results Fifty (26.5%) of the 189 women had cesarean deliveries. According to logistic regression analysis, maternal height ( P = 0.004), parity ( P = 0.005) and cervical length ( P = 0.016), but not Bishop score ( P = 0.920), were identified as independent predictors of cesarean delivery. A risk score based on a model of these three parameters was calculated for each patient. The model was shown to have an adequate goodness of fit ( P = 0.201) and the area under the curve was 0.722, indicating fairly good discrimination. Conclusions Maternal height, parity and cervical length were independent parameters for predicting the risk of cesarean delivery after labor induction in twin gestations. A predictive model using these parameters may provide useful information for deciding whether or not to induce labor. [ABSTRACT FROM AUTHOR]