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Objective: To investigate the effect of interpregnancy interval (IPI) on preterm birth (PTB) according to whether the previous birth was preterm or term. Design: Cohort study. Setting: USA (California), Australia, Finland, Norway (1980–2017). Population: Women who gave birth to first and second (n = 3 213 855) singleton livebirths. Methods: Odds ratios (ORs) for PTB according to IPIs were modelled using logistic regression with prognostic score stratification for potential confounders. Within‐site ORs were pooled by random effects meta‐analysis. Outcome measure: PTB (gestational age <37 weeks). Results: Absolute risk of PTB for each IPI was 3–6% after a previous term birth and 17–22% after previous PTB. ORs for PTB differed between previous term and preterm births in all countries (P‐for‐interaction ≤ 0.001). For women with a previous term birth, pooled ORs were increased for IPI <6 months (OR 1.50, 95% CI 1.43–1.58); 6–11 months (OR 1.10, 95% CI 1.04–1.16); 24–59 months (OR 1.16, 95% CI 1.13–1.18); and ≥ 60 months (OR 1.72, 95%CI 1.60–1.86), compared with 18–23 months. For previous PTB, ORs were increased for <6 months (OR 1.30, 95% CI 1.18–1.42) and ≥60 months (OR 1.29, 95% CI 1.17–1.42), but were less than ORs among women with a previous term birth (P < 0.05). Conclusions: Associations between IPI and PTB are modified by whether or not the previous pregnancy was preterm. ORs for short and long IPIs were higher among women with a previous term birth than a previous PTB, which for short IPI is consistent with the maternal depletion hypothesis. Given the high risk of recurrence and assuming a causal association between IPI and PTB, IPI remains a potentially modifiable risk factor for women with previous PTB. Short versus long interpregnancy intervals associated with higher ORs for preterm birth (PTB) after a previous PTB. Short versus long interpregnancy intervals associated with higher ORs for preterm birth (PTB) after a previous PTB. [ABSTRACT FROM AUTHOR]

Background: Interpregnancy interval (IPI) <6 months is a potentially modifiable risk factor for adverse perinatal health outcomes.Objective: This systematic review evaluated the international literature on the risk of perinatal death associated with IPI.Search Strategy: Two independent reviewers screened titles and abstracts identified in MEDLINE, EMBASE and Scopus from inception to 4 April 2019 (Prospero Registration #CRD42018092792).Selection Criteria: Studies were included if they provided a description of IPI measurement and perinatal death, including stillbirth and neonatal death.Data Collection and Analysis: A narrative review was performed for all included studies. Random effects meta-analysis was used to compare unadjusted odds of perinatal death associated with IPI <6 months and IPI ≥6 months. Analyses were performed by outcome of the preceding pregnancy and study location.Main Results: Of the 624 unique articles identified, 26 met the inclusion criteria. The pooled unadjusted odds ratio of perinatal death for IPI <6 months was 1.34 (95% CI 1.17-1.53) following a previous live birth, 0.85 (95% CI 0.73-0.99) following a previous miscarriage and 1.07 (95% CI 0.84-1.36) following a previous stillbirth compared with IPI ≥6 months. However, few high-income country studies reported an association after adjustment. Fewer studies evaluated the impact of long IPI on perinatal death and what evidence was available showed mixed results.Conclusions: Results suggest a possible association between short IPI and risk of perinatal death following a live birth, particularly in low- to middle-income countries.Tweetable Abstract: Short IPI <6 months after a live birth was associated with greater risk of perinatal death than IPI ≥6 months. [ABSTRACT FROM AUTHOR]

Objectives: We assessed whether interpregnancy interval (IPI) length after live birth and after pregnancy termination was associated with preterm birth (PTB).Design: Multiyear birth cohort.Settings: Fetal death, birth and infant death certificates in California merged with Office of Statewide Health Planning and Development.Population: One million California live births (2007-10) after live birth and after pregnancy termination.Methods: Logistic regression was used to estimate odds ratios (ORs) of PTB of 20-36 weeks of gestation and its subcategories for IPIs after a live birth and after a pregnancy termination. We used conditional logistic regression (two IPIs/mother) to investigate associations within mothers.Main Outcome Measure: PTB relative to gestations of ≥ 37 weeks.Results: Analyses included 971 211 women with IPI after live birth, and 138 405 women with IPI after pregnancy termination with 30.6% and 74.6% having intervals of <18 months, respectively. IPIs of <6 months or 6-11 months after live birth showed increased odds of PTB adjusted ORs for PTB of 1.71 (95% CI 1.65-1.78) and 1.20 (95% CI 1.16-1.24), respectively compared with intervals of 18-23 months. An IPI >36 months (versus 18-23 months) was associated with increased odds for PTB. Short IPI after pregnancy termination showed a decreased OR of 0.87 (95% CI 0.81-0.94). The within-mother analysis showed the association of increased odds of PTB for short IPI, but not for long IPI.Conclusions: Women with IPI <1 or >3 years after a live birth were at increased odds of PTB-an important group for intervention to reduce PTB. Short IPI after pregnancy termination was associated with reduced odds for PTB and needs to be further explored.Tweetable Abstract: Short and long IPI after live birth, but not after pregnancy termination, showed increased odds for PTB. [ABSTRACT FROM AUTHOR]

Objective: The objective of this study was to assess the presence of newly acquired preterm birth (PTB) risk factors among primiparous women with no prior history of PTB.Design: Case-control study.Setting: Deliveries occurring within a large healthcare system from 2002 to 2012.Population: Women with their first two consecutive pregnancies carried to ≥20(0/7)  weeks' gestation.Methods: Those delivering the first pregnancy at term and the second preterm ≥20(0/7) and <37(0/7)  weeks (term-preterm cases) were compared with women with a term birth in their first two pregnancies (term-term controls). Social factors with the potential to change between the first and second pregnancies and intrapartum labour characteristics in the first pregnancy were compared between cases and controls.Main Outcome Measures: Risk factors for term-preterm sequence.Results: About 38 215 women met inclusion criteria; 1353 (3.8%) were term-preterm cases. Cases and controls were similar with regard to race/ethnicity and maternal age at the time of the first and second deliveries. Cases delivered their second pregnancy approximately 3 weeks earlier (35.7 versus 39.1, P < 0.001). In multivariable models accounting for known PTB risk factors, women with a caesarean delivery in the first pregnancy [adjusted odds ratio (aOR) = 2.20; 95% confidence interval (CI) 1.57-3.08], new tobacco use (aOR = 2.33; 95% CI 1.61-3.38), and an interpregnancy interval <18 months (aOR = 1.37; 95% CI 1.21-1.55) were at increased risk of term-preterm sequence.Conclusion: Caesarean delivery in the first pregnancy, new tobacco use, and short interpregnancy interval <18 months are significant risk factors for term-preterm sequence. Women should receive postpartum counselling regarding appropriate interpregnancy interval and cessation of tobacco use.Tweetable Abstract: Caesarean delivery in the 1st pregnancy is a significant risk factor for preterm birth following a term delivery. [ABSTRACT FROM AUTHOR]

Objective: To examine the associations between interpregnancy interval and later maternal cardiovascular disease (CVD) risk.Design: Population-based record linkage study.Setting: New South Wales, Australia, 1994-2011.Population: 216 467 women having first and second liveborn singleton infants, excluding those with an existing or pregnancy-related CVD risk factor.Methods: We linked birth records of mothers to the mothers' subsequent CVD (coronary heart disease, cerebrovascular events, and chronic heart failure) hospitalisation or death. Multivariable Cox proportional hazard regression was used to estimate adjusted hazard ratios (AHR) [95% confidence interval (CI)], accounting for maternal age, parity, socioeconomic status, and smoking during pregnancy.Main Outcome Measures: The first occurrence of a CVD hospitalisation or death after the second birth.Results: In comparison with mothers with an interpregnancy interval of 18-23 months (reference category), the AHR among mothers with interpregnancy interval of <12 months was 1.56 (95% CI 1.18-2.07) and of 12-17 months was 1.13 (95% CI 0.84-1.51). The AHRs were 1.40 (95% CI 1.07-1.82), 1.87 (95% CI 1.21-2.89), and 3.41 (95% CI 1.07-10.91), corresponding to interpregnancy intervals of 24-59, 60-119, and ≥120 months, respectively. AHRs of specific CVD categories showed a similar pattern.Conclusions: Interpregnancy interval is associated with the risk of subsequent maternal CVD in a J-shaped fashion. The association is independent of the existing and pregnancy-related CVD risk factors analysed. Both short and long interpregnancy intervals can be used as risk markers to identify women with an elevated CVD risk later in life.Tweetable Abstract: Interpregnancy interval is associated with the risk of subsequent maternal cardiovascular disease in a J-shaped fashion. [ABSTRACT FROM AUTHOR]

Objective: To determine the relationship of interpregnancy interval with maternal and offspring outcomes.Design: Retrospective study with data from the Perinatal Information System database of the Latin American Centre for Perinatology and Human Development, Uruguay.Setting: Latin America, 1990-2009.Population: A cohort of 894 476 women delivering singleton infants.Methods: During 1990-2009 the Perinatal Information System database of the Latin American Centre for Perinatology identified 894 476 women with defined interpregnancy intervals: i.e. the time elapsed between the date of the previous delivery and the first day of the last normal menstrual period for the index pregnancy. Using the interval 12-23 months as the reference category, multiple logistic regression estimated adjusted odds ratios (aORs) with 95% confidence intervals (95% CIs) of the association between various interval lengths and maternal and offspring outcomes.Main Outcome Measures: Maternal death, pre-eclampsia, eclampsia, puerperal infection, fetal death, neonatal death, preterm birth, and low birthweight.Results: In the reference interval there was 0.05% maternal death, 1.00% postpartum haemorrhage, 2.80% pre-eclampsia, 0.15% eclampsia, 0.28% puerperal infection, 3.45% fetal death, 0.68% neonatal death, 12.33% preterm birth, and 9.73% low birthweight. Longer intervals had increased odds of pre-eclampsia (>72 months), fetal death (>108-119 months), and low birthweight (96-107 months). Short intervals of <12 months had increased odds of pre-eclampsia (aOR 0.80; 95% CI 0.76-0.85), neonatal death (aOR 1.18; 95% CI 1.08-1.28), and preterm birth (aOR 1.16; 95% CI 1.11-1.21). Statistically, the interval had no relationship with maternal death, eclampsia, and puerperal infection.Conclusions: A short interpregnancy interval of <12 months is associated with pre-eclampsia, neonatal mortality, and preterm birth, but not with other maternal or offspring outcomes. Longer intervals of >72 months are associated with pre-eclampsia, fetal death, and low birthweight, but not with other maternal or offspring outcomes.Tweetable Abstract: A short interpregnancy interval of <12 months is associated with neonatal mortality and preterm birth. [ABSTRACT FROM AUTHOR]

Objective: To examine the relationship between maternal characteristics, serum biomarkers and preterm birth (PTB) by spontaneous and medically indicated subtypes.Design: Population-based cohort.Setting: California, United States of America.Population: From a total population of 1 004 039 live singleton births in 2009 and 2010, 841 665 pregnancies with linked birth certificate and hospital discharge records were included.Methods: Characteristics were compared for term and preterm deliveries by PTB subtype using logistic regression and odds ratios adjusted for maternal characteristics and obstetric factors present in final stepwise models and 95% confidence intervals. First-trimester and second-trimester serum marker levels were analysed in a subset of 125 202 pregnancies with available first-trimester and second-trimester serum biomarker results.Main Outcome Measure: PTB by subtype.Results: In fully adjusted models, ten characteristics and three serum biomarkers were associated with increased risk in each PTB subtype (Black race/ethnicity, pre-existing hypertension with and without pre-eclampsia, gestational hypertension with pre-eclampsia, pre-existing diabetes, anaemia, previous PTB, one or two or more previous caesarean section(s), interpregnancy interval ≥ 60 months, low first-trimester pregnancy-associated plasma protein A, high second-trimester α-fetoprotein, and high second-trimester dimeric inhibin A). These risks occurred in 51.6-86.2% of all pregnancies ending in PTB depending on subtype. The highest risk observed was for medically indicated PTB <32 weeks in women with pre-existing hypertension and pre-eclampsia (adjusted odds ratio 89.7, 95% CI 27.3-111.2).Conclusions: Our findings suggest a shared aetiology across PTB subtypes. These commonalities point to targets for further study and exploration of risk reduction strategies.Tweetable Abstract: Findings suggest a shared aetiology across preterm birth subtypes. Patterns may inform risk reduction efforts. [ABSTRACT FROM AUTHOR]

Objective To examine the risk of pre-eclampsia ( PE) in women conceiving after assisted reproductive technologies ( ART). Potential confounding from maternal age, long intervals between births, new partner and smoking were evaluated. Design and setting Population-based cohort study with data from the Medical Birth Registry of Norway. Population A total of 501 766 mothers with offspring from 1988 to 2009. Methods Births to the same mother were linked in sibship data files with information of ART. Main outcome measures Odds ratio ( OR) (95% confidence intervals) of PE in pregnancies conceived by ART compared with spontaneous conception, stratified by parity. Results The prevalence of PE was 5.1% in first, 2.2% in second and 2.1% in third pregnancies. Corresponding figures in ART pregnancies were 6.0%, 3.3% and 4.4%. Hence, the odds ratios of PE in ART pregnancies relative to spontaneous pregnancies increased from 1.2 (1.1-1.3) in first, 1.5 (1.3-1.8) in second to 2.1 (1.4-3.3) in third pregnancies. Adjusting by maternal age lowered the odds ratio to 1.3 (1.1-1.6) and 1.8 (1.2-2.8) in second and third pregnancies, respectively. Multi-adjusted, birth interval had more impact than change of partner. Smoking was associated with a strongly reduced PE risk (odds ratio 0.65; 0.62-0.69), but there was no confounding by smoking on the ART associated risk. Conclusions Assisted reproductive technologies increases the risk of PE, and the risk may increase by parity. The association between ART pregnancies and PE is to some extent explained by interbirth intervals and advanced maternal age, but not to change of partner or smoking. [ABSTRACT FROM AUTHOR]

Objective To assess the influence of inadequate birth spacing on birth timing distribution across gestation. Design Population-based retrospective cohort study using vital statistics birth records. Setting Ohio, USA. Study Population Singleton, non-anomalous live births ≥20 weeks to multiparous mothers, 2006-2011. Methods Birth frequency at each gestational week was compared following short IPIs of <6, 6-12 and 12-18 months versus referent group, normal IPI ≥18 months. Main outcome measures Frequency of birth at each gestational week; preterm <37 weeks; <39 and ≥40 weeks. Results Of 454 716 births, 87% followed a normal IPI ≥18 months, 10.7% had IPI 12-18 months and 2.2% with IPI <12 months. The risk of delivery <39 weeks was higher following short IPI <12 months, adj OR (odds ratio) 2.78 (95% CI 2.64, 2.93). 53.3% of women delivered before the 39th week after IPI <12 months compared with 37.5% of women with normal IPI, P < 0.001. Likewise, birth at ≥40 weeks was decreased (16.9%) following short IPI <12 months compared to normal IPI, 23.2%, adj OR 0.67 (95% CI 0.64, 0.71). This resulted in a shift of the frequency distribution curve of birth by week of gestation to the left for pregnancies following a short IPI <12 months and 12-18 months compared to, birth spacing ≥18 months. Conclusions While short IPI is a known risk factor for preterm birth, our data show that inadequate birth spacing is associated with decreased gestational age for all births. Pregnancies following short IPIs have a higher frequency of birth at all weeks of gestation prior to 39 and fewer births ≥40 weeks, resulting in overall shortened pregnancy duration. [ABSTRACT FROM AUTHOR]

Objective To estimate the effects on pregnancy outcomes of the duration of the preceding interpregnancy interval (IPI) and type of pregnancy outcome that began the interval. Design Observational population-based study. Setting The Maternal Child Health–Family Planning (MCH–FP) area of Matlab, Bangladesh. Population A total of 66 759 pregnancy outcomes that occurred between 1982 and 2002. Methods Bivariate tabulations and multinomial logistic regression analysis. Main outcome measures Pregnancy outcomes (live birth, stillbirth, miscarriage [spontaneous fetal loss prior to 28 weeks], and induced abortion). Results When socio-economic and demographic covariates are controlled, of the IPIs that began with a live birth, those <6 months in duration were associated with a 7.5-fold increase in the odds of an induced abortion (95% CI 6.0–9.4), a 3.3-fold increase in the odds of a miscarriage (95% CI 2.8–3.9), and a 1.6-fold increase in the odds of a stillbirth (95% CI 1.2–2.1) compared with 27- to 50-month IPIs. IPIs of 6–14 months were associated with increased odds of induced abortion (2.0, 95% CI 1.5–2.6). IPIs ≥ 75 months were associated with increased odds of all three types of non-live-birth (NLB) outcomes but were not as risky as very short intervals. IPIs that began with a NLB were generally more likely to end with the same type of NLB. Conclusions Women whose pregnancies are between 15 and 75 months after a preceding pregnancy outcome (regardless of its type) have a lower likelihood of fetal loss than those with shorter or longer IPIs. Those with a preceding NLB outcome deserve special attention in counselling and monitoring. [ABSTRACT FROM AUTHOR]

Pregnancies conceived soon after the birth of a child are considered at increased risk for adverse outcomes, including preterm birth (Conde-Agudelo et al. As the interval from birth of the first child to conception of the second could not possibly have caused the birthweight of the first child, they concluded that short interval is a marker, rather than a cause of high-risk status. Using national data from Norway, they demonstrated that the birthweight of second-born children following a short interval was substantially lower than that of second-born children following a more typical interval. [Extracted from the article]

In a two-generation study of the nationwide 1958 British cohort and their offspring, we investigated the intergenerational influence of birth order on birthweight. Despite increases in own birthweight by birth order and a positive parent–offspring correlation in birthweights, there was a suggestion that parental birth order was inversely associated with offspring birthweight. This paradoxical finding was due to differential intergenerational birthweight associations, with a weaker association in later-born compared with first-born parents. Our findings suggest that underlying causes of a given birthweight should be taken into account in studies that investigate long term health outcomes. [ABSTRACT FROM AUTHOR]

The article presents commentaries on the study by BZ Shachar et al. on the increased odds of preterm birth (PTB) at less than thirty-seven weeks among women with an interpregnancy interval (IPI) of less than six months following a live birth. Topics include reference to comparison of less preterm birth episodes for IPI greater than eighteen months, population-based cohort study design as well as two interpregnancy intervals via maternally matched design concept.

In this article, the author comments on an article by author A.D. Ngo on a study regarding effects of inter-pregnancy interval that was published in the periodical in the July 2016 issue. Topics discussed include suggesting a relationship between cardiovascular disease and inter-pregnancy interval, linking of use of oral contraceptive to cardiovascular disease risk and using administrative data which might not contain information regarding stillbirth, miscarriage and abortion.

The author presents a commentary on the article "Influence of Interpregnancy Interval on Birth Timing," published within the issue. He studies the connection between the short interpregnancy intervals (IPIs) and an increased rate of preterm birth in the next pregnancy by analysing the mentioned article.