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Interpregnancy interval and adverse pregnancy outcomes among pregnancies following miscarriages or induced abortions in Norway (2008-2016): a cohort study. Interpregnancy interval (IPI), or the time between the end of one pregnancy and the conception of the next pregnancy, has been associated with an increased risk of adverse pregnancy outcomes. The "ins" and "outs" of interpregnancy interval effects: Who contributes, and does it matter?. [Extracted from the article]

Background: Short and long interpregnancy intervals (IPI) are associated with increased risk of hypertensive disorders of pregnancy, yet whether this association is modified by maternal age remains unclear. Objectives: To examine if the association between IPI and hypertensive disorders of pregnancy varies by maternal age at birth prior to IPI. Methods: We conducted a population‐based cohort study of all mothers who had their first two (n = 169 896) consecutive births in Western Australia (WA) between 1980 and 2015. We estimated the risk of preeclampsia and gestational hypertension for 6 to 60 months of IPI according to maternal age at birth prior to IPI (<20 years, 20‐24, 25‐29, 30‐34 and ≥35 years). We modelled IPI using restricted cubic splines and reported adjusted relative risk (RRs) with 95% CI at 6, 12, 24, 36, 48 and 60 months, with 18 months as reference. Results: The risk of preeclampsia was increased at longer IPIs (60 months) compared to 18 months for mothers 35 years or older (RR 2.19, 95% confidence interval (CI) 1.14, 4.18) and to a lesser extent for mothers 30‐ to 34 years old (RR 1.43, 95% CI 1.10, 1.84). Compared to 18 months, the risk of preeclampsia was lower at 12 months of IPI for mothers younger than 20 years (RR 0.74, 95% CI 0.57, 0.96), but not for mothers 35 years or older (RR 0.62, 95% CI 0.36, 1.07). There was insufficient evidence for increased risk of hypertensive disorders of pregnancy at shorter IPIs of <18 months for mothers of all ages. Conclusions: Our findings challenge the "one size fits all" recommendation for an optimal IPI, and a more tailored approach to family planning counselling may be required to improve health. [ABSTRACT FROM AUTHOR]

Background: There is much interest in how the length of the previous birth interval affects various child outcomes, and it has become increasingly common to estimate such effects from sibling models. This is because one then controls for unobserved determinants of the outcome that are shared between the siblings and linked to the birth interval length. However, it is a common idea that such effects can only be estimated from data on families with three or more children. Objective: The goal of this paper is to show, through an intuitive argument and a simulation experiment, that it is possible to estimate effects of birth interval only from families with two children. Methods: Observations are simulated from two equations for fertility and one equation for child mortality. The fertility equations include a random term that is assumed to be correlated with the random term in the mortality equation. Mortality models are then estimated from the simulated observations. This is done 1000 times, and the averages of the 1000 sets of estimates are calculated. Results: The simulation experiment illustrates that it is indeed possible (by using a model specification that takes into account that no birth interval is defined for the first birth) to estimate birth interval effects in sibling models even when the data include only families with two children. Conclusion: It is good news that families with only two children can contribute to the estimation of birth interval effects. This is because, with a broader basis for the estimation, the precision is improved and there is less reason for concern about the general relevance of the estimates. An important limitation, however, is that it is potentially problematic to control for maternal age in a sibling model estimated only for the first and second child. [ABSTRACT FROM AUTHOR]

The article offers information on associations between interpregnancy interval and severe maternal morbidity types. Topics discussed include impact of factors such as maternal age, pregnancy intention, socioeconomic status or outcome of the index pregnancy on adverse outcomes; role of heterogeneity in birth spacing counselling; and impact on analyses of interpregnancy interval and severe maternal morbidity due to limitations of the U.S. vital statistics data.

An editorial is presented on advancing the methodological quality of studies on short birth spacing and discussing key areas for future work. Topics include an assessment of the methodological quality of existing studies on short birth spacing and adverse pregnancy outcomes; arising through mis-timed measurement of time-varying confounders such as maternal age, socio-economic status, or smoking.

Background: Several studies have examined the association between IPI and birth outcomes, but few have explored the association between interpregnancy interval (IPI) and postnatal outcomes.Objective: We examined the association between IPI and injury-related infant mortality, a leading cause of postneonatal mortality.Methods: We used 2011-2015 US period-linked birth-infant death vital statistics data to generate a multiyear birth cohort of non-first-born singleton births (N = 9 782 029). IPI was defined as the number of months between a live birth and the start of the pregnancy leading to the next live birth. Causes of death in the first year of life were identified using ICD-10 codes. Hazard ratios (HR) for IPI categories were estimated using Cox proportional hazards models adjusted for birth order, county poverty level, and maternal characteristics (marital status, race/ethnicity, education, age at previous birth).Results: After adjustment, overall infant mortality (48.1 per 10 000 births) was higher for short and long IPIs compared with IPI 18-23 months (reference): <6, aHR 1.61, 95% CI 1.54, 1.68; 6-11, aHR 1.22, 95% CI 1.17, 1.26; and 60+ months, aHR 1.12, 95% CI 1.08, 1.16. In comparison, the risk of injury-related infant mortality (4.4 per 10 000 births) decreased with longer IPIs: <6, aHR 1.77, 95% CI 1.55, 2.01; 6-11, aHR 1.41, 95% CI 1.25, 1.59; 12-17, aHR 1.25, 95% CI 1.10, 1.41; 24-59, aHR 0.78, 95% CI 0.69, 0.87; and 60+ months, aHR 0.55, 95% CI 0.48, 0.62.Conclusion: Unlike overall infant mortality, injury-related infant mortality decreased with IPI length. While injury-related deaths are rare, these patterns suggest that the timing between births may be a marker of risk for fatal infant injuries. The first year postpartum may be an ideal time for the delivery of evidence-based injury prevention programmes as well as family planning services. [ABSTRACT FROM AUTHOR]

The article discusses the effects of short pregnancy spacing on maternal nutrition and adverse pregnancy outcomes such as preterm birth for women in the U.S. According to the author, the use of contraception has been recommended to women and family planning providers by the Centers for Disease Control and Prevention (CDC).

Background: Numerous studies use birth certificate data to examine the association between interpregnancy interval (IPI) and maternal and perinatal health outcomes. Substantive changes from the latest birth certificate revision have implications for examining this relationship.Methods: We provide an overview of the National Vital Statistics System and recent changes to the national birth certificate data file, which have implications for assessing IPI and perinatal health outcomes. We describe the calculation of IPI using birth certificate information and related measurement issues. Missing IPI values by maternal age, race and education using 2016 birth certificate data were also compared. Finally, we review and summarise data quality studies of select covariate and outcome variables (sociodemographic, maternal health and health behaviours, and infant health) conducted after the most recent 2003 birth certificate revision.Results: Substantive changes to data collection, dissemination and quality have occurred since the 2003 revision. These changes impact IPI measurement, trends and associations with perinatal health outcomes. Missing values of IPI were highest for older ages, lower education and non-Hispanic black women. Minimal differences were found when comparing IPI using different gestational age measures. Recent data quality studies pointed to substantial variation in data quality by item and across states.Conclusion: Future studies examining the association of IPI with maternal and perinatal data using vital records should consider these aspects of the data in their research plan, sensitivity analyses and interpretation of findings. [ABSTRACT FROM AUTHOR]

Background: Currently, no federal guidelines provide recommendations on healthy birth spacing for women in the United States. This systematic review summarises associations between short interpregnancy intervals and adverse maternal outcomes to inform the development of birth spacing recommendations for the United States.Methods: PubMed/Medline, POPLINE, EMBASE, CINAHL, the Cochrane Database of Systematic Reviews, and a previous systematic review were searched to identify relevant articles published from 1 January 2006 and 1 May 2017. Included studies reported maternal health outcomes following a short versus longer interpregnancy interval, were conducted in high-resource settings, and adjusted estimates for at least maternal age. Two investigators independently assessed study quality and applicability using established methods.Results: Seven cohort studies met inclusion criteria. There was limited but consistent evidence that short interpregnancy interval is associated with increased risk of precipitous labour and decreased risks of labour dystocia. There was some evidence that short interpregnancy interval is associated with increased risks of subsequent pre-pregnancy obesity and gestational diabetes, and decreased risk of preeclampsia. Among women with a previous caesarean delivery, short interpregnancy interval was associated with increased risk of uterine rupture in one study. No studies reported outcomes related to maternal depression, interpregnancy weight gain, maternal anaemia, or maternal mortality.Conclusions: In studies from high-resource settings, short interpregnancy intervals are associated with both increased and decreased risks of adverse maternal outcomes. However, most outcomes were evaluated in single studies, and the strength of evidence supporting associations is low. [ABSTRACT FROM AUTHOR]

Background: Meta-analyses of observational studies have shown that women with a shorter interpregnancy interval (the time from delivery to start of a subsequent pregnancy) are more likely to experience adverse pregnancy outcomes, such as preterm delivery or small for gestational age birth, than women who space their births further apart. However, the studies used to inform these estimates have methodological shortcomings.Methods: In this commentary, we summarise the discussions of an expert workgroup describing good practices for the design, analysis, and interpretation of observational studies of interpregnancy interval and adverse perinatal health outcomes.Results: We argue that inferences drawn from research in this field will be improved by careful attention to elements such as: (a) refining the research question to clarify whether the goal is to estimate a causal effect vs describe patterns of association; (b) using directed acyclic graphs to represent potential causal networks and guide the analytic plan of studies seeking to estimate causal effects; (c) assessing how miscarriages and pregnancy terminations may have influenced interpregnancy interval classifications; (d) specifying how key factors such as previous pregnancy loss, pregnancy intention, and maternal socio-economic position will be considered; and (e) examining if the association between interpregnancy interval and perinatal outcome differs by factors such as maternal age.Conclusion: This commentary outlines the discussions of this recent expert workgroup, and describes several suggested principles for study design and analysis that could mitigate many potential sources of bias. [ABSTRACT FROM AUTHOR]

Background: Previous studies have demonstrated that short interpregnancy interval (the interval between delivery and estimated last menstrual period of a subsequent pregnancy) is associated with small for gestational age birth. It is controversial if this association is causal, as few studies have accounted for likely confounding factors such as unintended pregnancy. We examined the association between interpregnancy interval and infant birthweight, adjusting for pregnancy intention and other socio-economic and obstetrical risk factors.Methods: We used data from the Scandinavian Successive Small-for-Gestational-Age births study (1986-1988). Birthweight was expressed as a gestational age-standardised z-score.Results: Among 1406 women, a trend towards lower birthweight z-score with short interpregnancy interval was not statistically significant (unadjusted difference in birthweight z-score of -0.25, 95% confidence interval (CI) -0.55, 0.05). After adjusting for pregnancy intention, detailed measures of socio-economic status, and other covariates, the estimated magnitude of effect between interpregnancy interval and birthweight z-score was further attenuated (adjusted difference in birthweight z-score of -0.13, 95% CI -0.46, 0.20).Conclusions: In this cohort study with detailed information on pregnancy intention and socio-economic status, short interpregnancy interval was not associated with lower birthweight. These findings suggest that previously observed associations between short interpregnancy interval and lower birthweight may reflect confounding by socio-economic and/or other unmeasured confounders. [ABSTRACT FROM AUTHOR]

Background: This systematic review summarises association between short interpregnancy intervals and adverse perinatal health outcomes in high-resource settings to inform recommendations for healthy birth spacing for the United States.Methods: Five databases and a previous systematic review were searched for relevant articles published between 1966 and 1 May 2017. We included studies meeting the following criteria: (a) reporting of perinatal health outcomes after a short interpregnancy interval since last livebirth; (b) conducted within a high-resource setting; and (c) estimates were adjusted for maternal age and at least one socio-economic factor.Results: Nine good-quality and 18 fair-quality studies were identified. Interpregnancy intervals <6 months were associated with a clinically and statistically significant increased risk of adverse outcomes in studies of preterm birth (eg, aOR ≥ 1.20 in 10 of 14 studies); spontaneous preterm birth (eg, aOR ≥ 1.20 in one of two studies); small-for-gestational age (eg, aOR ≥ 1.20 in 5 of 11 studies); and infant mortality (eg, aOR ≥ 1.20 in four of four studies), while four studies of perinatal death showed no association. Interpregnancy intervals of 6-11 and 12-17 months generally had smaller point estimates and confidence intervals that included the null. Most studies were population-based and few included adjustment for detailed measures of key confounders.Conclusions: In high-resource settings, there is some evidence showing interpregnancy intervals <6 months since last livebirth are associated with increased risks for preterm birth, small-for-gestational age and infant death; however, results were inconsistent. Additional research controlling for confounding would further inform recommendations for healthy birth spacing for the United States. [ABSTRACT FROM AUTHOR]

Background: The World Health Organization (WHO) recommends that women wait at least 24 months after a livebirth before attempting a subsequent pregnancy to reduce the risk of adverse maternal, perinatal, and infant health outcomes. However, the applicability of the WHO recommendations for women in the United States is unclear, as breast feeding, nutrition, maternal age at first birth, and total fertility rate differs substantially between the United States and the low- and middle-resource countries upon which most of the evidence is based.Methods: To inform guideline development for birth spacing specific to women in the United States, the Office of Population Affairs (OPA) convened an expert work group meeting in Washington, DC, on 14-15 September 2017 among reproductive, perinatal, paediatric, social, and public health epidemiologists; obstetrician-gynaecologists; biostatisticians; and experts in evidence synthesis related to women's health.Results: Presentations and discussion topics included the methodological quality of existing studies, evaluation of the evidence for causal effects of short interpregnancy intervals on adverse perinatal and maternal health outcomes, good practices for future research, and identification of research gaps and priorities for future work.Conclusions: This report provides an overview of the presentations, discussions, and conclusions from the expert work group meeting. [ABSTRACT FROM AUTHOR]

Background: Short interpregnancy intervals (IPI) are associated with poor birth outcomes. Often, only livebirths are considered to estimate IPI. The objective of our work is to explore whether the associations between demographic, behavioural, and pregnancy variables and IPI change when events other than livebirth are included.Methods: We used data from the 2006-10 and 2011-13 period of the National Survey of Family Growth (NSFG). We defined IPI using the conception date of the index pregnancy and the event date of the previous one ending in (i) livebirth; (ii) stillbirth; (iii) miscarriage; (iv) abortion; or (v) any of these events. Risk ratios (RR) were estimated for short IPI (<18 months), and demographic, pregnancy, and behavioural variables using log-linear models.Results: When intervening events are included, the association between short IPI and its predictors vary by definition, especially for unintended versus intended pregnancies (only livebirth risk ratio [RR] 1.34, 95% confidence interval [CI] 1.2, 1.5) versus livebirth and miscarriage RR 1.14, 95% CI 1.0, 1.3) and women older than 30 vs. younger than 20 at resolution of the previous pregnancy (only livebirth RR 1.22, 95% CI 1.0, 1.5 versus livebirth and miscarriage RR 1.36, 95% CI 1.2, 1.6).Conclusions: Including miscarriage as an intervening event in the calculation of IPI changes the association between several risk factors and short IPI. However, the association between short IPI and preterm birth does not vary when different IPI calculations are used. [ABSTRACT FROM AUTHOR]

The article comments on the evaluation of the association between interpregnancy, live birth to subsequent conception interval (IPI) and infant mortality. Topics include the study's focus on injury‐related and general external cause mortality; short intervals that were associated with elevated risk of all types of mortality.

The article presents studies on the association between adverse perinatal outcomes and birth spacing. A study of women in China shows a J-shaped relationship for preterm birth and interpregnancy interval the same to that observed in the U.S. and other settings. Another study discovered that the link between preterm birth and short interpregnancy interval was consistent across various definitions of interpregnancy.

de Moura DR, Costa JC, Santos IS, Barros AJD, Matijasevich A, Halpern R, Dumith S, Karam S, Barros FC. Risk factors for suspected developmental delay at age 2 years in a Brazilian birth cohort. Paediatric and Perinatal Epidemiology 2010; 24: 211–221. Many children are at risk of not achieving their full potential for development. Epidemiological studies have the advantage of being able to identify a number of associated factors potentially amenable to intervention. Our purpose was to identify risk factors for suspected developmental delay (SDD) at age 2 years among all children born in the city of Pelotas, Brazil, in 2004. This study was part of the 2004 Pelotas Birth Cohort. The Battelle Screening Developmental Inventory (BSDI) was administered to cohort children at age 2 years. A hierarchical model of determination for SDD with confounder adjustment was built including maternal sociodemographic, reproductive and gestational characteristics, as well as child and environmental characteristics. Multivariable analysis was carried out using Poisson regression. Prevalence ratios (PR) and 95% confidence intervals [95% CI] were calculated. In the results, 3.3% of the 3869 children studied screened positive for SDD. After confounder control, children more likely to show SDD were: those with positive BSDI at age 12 months (PR = 5.51 [3.59, 8.47]); with 5-min Apgar <7 (PR = 3.52 [1.70, 7.27]); with mothers who had <4 years of schooling (PR = 3.35 [1.98, 5.66]); from social classes D and E (PR = 3.00 [1.45, 6.19]); with a history of gestational diabetes (PR = 2.77 [1.34, 5.75]); born <24 months after the last sibling (PR = 2.46 [1.42, 4.27]); were not told child stories in the preceding week (PR 2.28 [1.43, 3.63]); did not have children's literature at home (PR = 2.08 [1.27, 3.39]); with low birthweight (PR = 1.75 [1.00, 3.07]); were born preterm (PR = 1.74 [1.07, 2.81]); with <6 antenatal care appointments (PR = 1.70 [1.07, 2.68]); with history of hospitalisation (PR = 1.65 [1.09, 2.50]); and of male sex (PR = 1.43 [1.00, 2.04]). These risk factors may constitute potential targets for intervention by public policies and may provide help to paediatricians in preventing developmental delay. [ABSTRACT FROM AUTHOR]

The objective of the study was to estimate and compare the correlation coefficients of head circumference and weight at birth among sibling pairs. Pairs of singleton siblings were ascertained among children born in Norway to the same mother between 1978 and 1997. Head circumference, birthweight and other perinatal factors were registered in the Medical Birth Registry of Norway. Head circumference measurements were obtained for first- and second-born in 287 448 sibling pairs. The correlation coefficient of head circumference among first- and second-born siblings was 0.343 (standard error 0.002) compared with 0.477 (standard error 0.002) for birthweight. These results were similar for later-born sibling pairs and only slightly influenced by other factors such as sex, fatherhood and time between pregnancies. Sensitivity analyses showed that substantial measurement error is required to explain the lower correlation for head circumference. In conclusion, the sibling correlation of head circumference was consistently weaker than that of birthweight. [ABSTRACT FROM AUTHOR]

In a historical follow-up study, we evaluated the association of the fertility of daughters with five perinatal factors: short (< 15 months) or long (> or = 45 months) preceding birth interval, low (< or = 20 years) or advanced (> or = 40 years) maternal age and season of birth. We used data concerning 2062 women married before the age of 31 and born in the Saguenay region of Quebec, Canada, between 1850 and 1899. Time between the wedding and first birth was used for the estimation of differences in fertility. Using logistic regression and controlling for several potential confounders, we found a slightly increased risk of monthly failure of conception for daughters born after a short but not for those born after a long birth interval (odds ratios [ORs] 1.09 [0.89, 1.33] and 0.87 [0.65, 1.16], respectively, with intervals between 21 and 32 months as the reference category). A slightly increased risk of conceptive failure was also seen for daughters of younger and older mothers (ORs 1.08 [0.89, 1.30] and 1.11 [0.91, 1.35], respectively, compared with maternal age between 24 and 30 years as the reference category). Fertility varied by season of birth (P = 0.02), with summer-born daughters having lowest and winter-born daughters having highest fertility. These results are consistent with the idea that maternal factors before or around birth play a role in the aetiology of reduced fertility. The data, however, do not unequivocally support the hypothesis that gave rise to the present study, namely that ovarian development may be disturbed after conception in conditions with an increased risk of maternal menstrual cycle irregularities. [ABSTRACT FROM AUTHOR]

A correction is presented to the article "Good practices for the design, analysis, and interpretation of observational studies on birth spacing and perinatal health outcomes" which appeared in the previous issue of the periodical.

Investigates the association between short conception intervals with poor infant outcomes in Minnesota. Performance of multivariate analyses; Impact of maternal age, marital status and educational attainment.