Effect of Interpregnancy Interval on Adverse Perinatal Outcomes in Southern China: A Retrospective Cohort Study, 2000-2015

Interpregnancy interval, air pollution, and the risk of low birth weight: a retrospective study in China

BACKGROUND

Both interpregnancy intervals (IPI) and environmental factors might contribute to low birth weight (LBW). However, the extent to which air pollution influences the effect of IPIs on LBW remains unclear. We aimed to investigate whether IPI and air pollution jointly affect LBW.

METHODS

A retrospective cohort study was designed in this study. The data of birth records was collected from the Jiangsu Maternal Child Information System, covering January 2020 to June 2021 in Nantong city, China. IPI was defined as the duration between the delivery date for last live birth and date of LMP for the subsequent birth. The maternal exposure to ambient air pollutants during pregnancy-including particulate matter (PM) with an aerodynamic diameter of ≤ 2.5 μm (PM2.5), PM10, ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2) and carbon monoxide (CO)-was estimated using a hybrid kriging-LUR-RF model. A novel air pollution score was proposed, assessing combined exposure to five pollutants (excluding CO) by summing their concentrations, weighted by LBW regression coefficients. Multivariate logistic regression models were used to estimate the effects of IPI, air pollution and their interactions on LBW. Relative excess risk due to interaction (RERI), attributable proportion of interaction (AP) and synergy index (S) were utilized to assess the additive interaction.

RESULTS

Among 10, 512 singleton live births, the LBW rate was 3.7%. The IPI-LBW risk curve exhibited an L-shaped pattern. The odds ratios (ORs) for LBW for each interquartile range increase in PM2.5, PM10, O3 and the air pollution score were 1.16 (95% CI: 1.01-1.32), 1.30 (1.06-1.59), 1.22 (1.06-1.41), and 1.32 (1.10-1.60) during the entire pregnancy, respectively. An additive interaction between IPI and PM2.5 was noted during the first trimester. Compared to records with normal IPI and low PM2.5 exposure, those with short IPI and high PM2.5 exposure had the highest risk of LBW (relative risk = 3.53, 95% CI: 1.85-6.49, first trimester).

CONCLUSION

The study demonstrates a synergistic effect of interpregnancy interval and air pollution on LBW, indicating that rational birth spacing and air pollution control can jointly improve LBW outcomes.

The prevalence of short inter-pregnancy interval and its associated risk factors among women attending primary health care centers of NGHA in Jeddah, Saudi Arabia: A cross-sectional study

Background

The inter-pregnancy interval (IPI) refers to the time between one pregnancy and the next. Studies have shown that IPIs shorter than 18 months are linked to negative outcomes, such as preterm delivery, infant mortality, and small-for-gestational-age birth. The aim of this study was to measure the prevalence and risk factors of short inter-pregnancy intervals among women receiving care at primary health centers in Jeddah, Saudi Arabia.

Methods and Material

This is a cross-sectional study conducted at primary health care centers among mothers with a history of giving birth to at least one child and having two successive pregnancies. The data was collected through face-to-face interviews using a structured questionnaire. Statistical analysis was carried out using RStudio (R version 4.3.0).

Results

A total of 300 responses were analyzed. The prevalence of short IPI was 36.0%, 31.0% had prolonged IPI, and 33.0% had optimal IPI. Lower educational level, unemployment as a student, low or middle income, a rise in the number of children, typically more than six, and an increase in the number of male offspring, mostly four or more, lack of breastfeeding, and breastfeeding duration have all been identified as statistically significant risk factors for short IPIs.

Conclusions

Short inter-pregnancy interval is prevalent in Jeddah city, which can negatively impact the perinatal outcomes. Addressing the risk factors and providing proper education in antenatal and postnatal clinics to reduce the number of unintended pregnancies can help in decreasing the number of short inter-pregnancy intervals and improving maternal and fetal outcomes.

Effects of short inter-pregnancy/birth interval on adverse perinatal outcomes in Asia-Pacific region: A systematic review and meta-analysis

BACKGROUND

Short inter-pregnancy or birth interval is associated with an increased risk of adverse perinatal outcomes. However, some emerging evidence questions this association and there are also inconsistencies among the existing findings. This study aimed to systematically review the evidence regarding the effect of short inter-pregnancy or birth intervals on adverse perinatal outcomes in the Asia-Pacific region.

METHODS

A comprehensive search of five databases was conducted targeting studies published between 2000 to 2023. Studies that reported on short inter-pregnancy or birth interval and examined adverse perinatal outcomes, such as low birthweight (LBW) preterm birth (PTB), small for gestational age (SGA), and neonatal mortality were included and appraised for methodological quality using the Joanna Briggs Institute critical appraisal tools. Three reviewers independently screened the studies and performed data extraction. Narrative synthesis and meta-analyses were conducted to summarise the key findings.

RESULTS

A total of 41 studies that fulfilled the inclusion criteria were included. A short-interpregnancy interval was associated with an increased risk of low birthweight (odds ratio [OR] = 1.65; 95%CI:1.39, 1.95), preterm birth (OR = 1.50; 95%CI: 1.35, 1.66), and small for gestational age (OR = 1.24; 95%CI:1.09, 1.41). We also found elevated odds of early neonatal mortality (OR = 1.91; 95%CI: 1.11, 3.29) and neonatal mortality (OR = 1.78; 95%CI: 1.25, 2.55) among women with short birth intervals.

CONCLUSION

This review indicates that both short inter-pregnancy and birth interval increased the risk of adverse perinatal outcomes. This underscores the importance of advocating for and implementing strategies to promote optimal pregnancy and birth spacing to reduce the occurrence of adverse perinatal outcomes. Reproductive health policies and programs need to be further strengthened and promote access to comprehensive family planning services and increase awareness about the importance of optimal pregnancy and birth spacing.

Association of interpregnancy interval and risk of adverse pregnancy outcomes in woman by different previous gestational ages

BACKGROUND

With an increasing proportion of multiparas, proper interpregnancy intervals (IPIs) are urgently needed. However, the association between IPIs and adverse perinatal outcomes has always been debated. This study aimed to explore the association between IPIs and adverse outcomes in different fertility policy periods and for different previous gestational ages.

METHODS

We used individual data from China's National Maternal Near Miss Surveillance System between 2014 and 2019. Multivariable Poisson models with restricted cubic splines were used. Each adverse outcome was analyzed separately in the overall model and stratified models. The stratified models included different categories of fertility policy periods (2014-2015, 2016-2017, and 2018-2019) and infant gestational age in previous pregnancy (<28 weeks, 28-36 weeks, and ≥37 weeks).

RESULTS

There were 781,731 pregnancies enrolled in this study. A short IPI (≤6 months) was associated with an increased risk of preterm birth (OR [95% CI]: 1.63 [1.55, 1.71] for vaginal delivery [VD] and 1.10 [1.03, 1.19] for cesarean section [CS]), low Apgar scores and small for gestational age (SGA), and a decreased risk of diabetes mellitus in pregnancy, preeclampsia or eclampsia, and gestational hypertension. A long IPI (≥60 months) was associated with an increased risk of preterm birth (OR [95% CI]: 1.18 [1.11, 1.26] for VD and 1.39 [1.32, 1.47] for CS), placenta previa, postpartum hemorrhage, diabetes mellitus in pregnancy, preeclampsia or eclampsia, and gestational hypertension. Fertility policy changes had little effect on the association of IPIs and adverse maternal and neonatal outcomes. The estimated risk of preterm birth, low Apgar scores, SGA, diabetes mellitus in pregnancy, and gestational hypertension was more profound among women with previous term births than among those with preterm births or pregnancy loss.

CONCLUSION

For pregnant women with shorter or longer IPIs, more targeted health care measures during pregnancy should be formulated according to infant gestational age in previous pregnancy.

Association between interpregnancy interval and gestational diabetes mellitus: A cohort study of the National Vital Statistics System 2020

OBJECTIVE

To assess the association between interpregnancy interval (IPI) and gestational diabetes mellitus (GDM).

METHODS

Data of this retrospective cohort study were obtained from the National Vital Statistics System (NVSS) 2020. The participants were divided into different groups according to different IPI (<6, 6-11, 12-17, 18-23, 24-59 (reference), 60-119, ≥120 months). Multivariate logistic models were constructed to evaluate the association between IPI and GDM. Subgroup analysis was further performed.

RESULTS

A total of 1 515 263 women were included, with 123 951 (8.18%) having GDM. Compared with the 24-59 months group, the <6 months (odds ratio [OR] 0.64, 95% confidence interval [CI] 0.46-0.90, P = 0.009), 12-17 months (OR 0.96, 95% CI 0.94-0.98, P < 0.001), and 18-23 months (OR 0.94, 95% CI 0.93-0.96, P < 0.001) groups had a significantly lower risk of GDM, while the 60-119 months (OR 1.13, 95% CI 1.11-1.15, P < 0.001) and ≥120 months (OR 1.18, 95% CI 1.15-1.21, P < 0.001) groups had a significantly higher risk of GDM. No significant difference was observed in the risk of GDM between the 6-11 and 24-59 months groups (P = 0.542). The PI-GDM association varied across different groups of age, pre-pregnancy body mass index, pre-pregnancy smoking status, history of cesarean section, history of preterm birth, prior terminations, and parity.

CONCLUSION

An IPI of 18-23 months may be a better interval than 24-59 months in managing the risk of GDM.

Association between short inter-pregnancy interval and placenta previa and placenta accreta spectrum with respect to maternal age at first cesarean delivery

OBJECTIVE

To explore the association between inter-pregnancy intervals and placenta previa and placenta accreta spectrum among women who had prior cesarean deliveries with respect to maternal age at first cesarean delivery.

METHODS

This retrospective study included clinical data from 9981 singleton pregnant women with a history of cesarean delivery at 11 public tertiary hospitals in seven provinces of China between January 2017 and December 2017. The study population was divided into four groups (<2, 2-5, 5-10, ≥10 years of the interval) according to the inter-pregnancy interval. The rate of placenta previa and placenta accreta spectrum among the four groups was compared, and multivariate logistic regression was used to analyze the relationship between inter-pregnancy interval and placenta previa and placenta accreta spectrum with respect to maternal age at first cesarean delivery.

RESULTS

Compared to women aged 30-34 years old at first cesarean delivery, the risk of placenta previa (aRR, 1.48; 95% CI, 1.16-1.88) and placenta accreta spectrum (aRR, 1.74; 95% CI, 1.28-2.35) were higher among women aged 18-24. Multivariate regression results showed that women at 18-24 with <2 years intervals exhibited a 5.05-fold increased risk for placenta previa compared with those with 2-5-year intervals (aRR, 5.05; 95% CI, 1.13-22.51). In addition, women aged 18-24 with less than 2 years intervals had an 8.44 times greater risk of developing PAS than women aged 30-34 with 2 to 5 years intervals (aRR, 8.44; 95% CI, 1.82-39.26).

CONCLUSIONS

The findings of this study suggested that short inter-pregnancy intervals were associated with increased risks for placenta previa, and placenta accreta spectrum for women under 25 years at first cesarean delivery, which may be partly attributed to obstetrical outcomes.

Interactions between long interpregnancy interval and advanced maternal age on neonatal outcomes

BACKGROUND

After the implementation of the universal two-child policy in China, it was more frequent to have long interpregnancy intervals (IPIs) and advanced maternal age. However, the interactions between long IPIs and advanced maternal age on neonatal outcomes are unknown.

METHODS

The study subjects of this historical cohort study were multiparas with singleton live births between October 1st, 2015, and October 31st, 2020. IPI was defined as the interval between delivery and conception of the subsequent pregnancy. Logistic regression models were used to calculate adjusted odds ratios (aORs) and 95% confidence intervals (CIs) of the risks of preterm birth (PTB), low birth weight (LBW), small for gestation age, and 1-min Apgar score ≤ 7 in different IPI groups. Relative excess risk due to interaction (RERI) was used to evaluate the additive interaction between long IPIs and advanced maternal age.

RESULTS

Compared with the 24 ≤ IPI ≤ 59 months group, the long IPI group (IPI ≥ 60 months) was associated with a higher risk of PTB (aOR, 1.27; 95% CI: 1.07-1.50), LBW (aOR, 1.32; 95% CI 1.08-1.61), and one-minute Apgar score ≤ 7 (aOR, 1.46; 95% CI 1.07-1.98). Negative additive interactions (all RERIs < 0) existed between long IPIs and advanced maternal age for these neonatal outcomes. Meanwhile, IPI < 12 months was also associated with PTB (aOR, 1.51; 95% CI 1.13-2.01), LBW (aOR, 1.50; 95% CI 1.09-2.07), and 1-min Apgar score ≤ 7 (aOR, 1.93; 95% CI 1.23-3.04).

CONCLUSIONS

Both short and long IPIs are associated with an increased risk of adverse neonatal outcomes. Appropriate IPI should be recommended to women planning to become pregnant again. In addition, better antenatal care might be taken to balance the inferiority of advanced maternal age and to improve neonatal outcomes.

Birth spacing and risk of adverse pregnancy and birth outcomes: A systematic review and dose-response meta-analysis

INTRODUCTION

The association between extreme birth spacing and adverse outcomes is controversial, and available evidence is fragmented into different classifications of birth spacing.

MATERIAL AND METHODS

We conducted a systematic review of observational studies to evaluate the association between birth spacing (i.e., interpregnancy interval and interoutcome interval) and adverse outcomes (i.e., pregnancy complications, adverse birth outcomes). Pooled odds ratios (ORs) with 95% confidence intervals (CI) were calculated using a random-effects model, and the dose-response relationships were evaluated using generalized least squares trend estimation.

RESULTS

A total of 129 studies involving 46 874 843 pregnancies were included. In the general population, compared with an interpregnancy interval of 18-23 months, extreme intervals (<6 months and ≥ 60 months) were associated with an increased risk of adverse outcomes, including preterm birth, small for gestational age, low birthweight, fetal death, birth defects, early neonatal death, and premature rupture of fetal membranes (pooled OR range: 1.08-1.56; p < 0.05). The dose-response analyses further confirmed these J-shaped relationships (pnon-linear  < 0.001-0.009). Long interpregnancy interval was only associated with an increased risk of preeclampsia and gestational diabetes (pnon-linear  < 0.005 and pnon-linear  < 0.001, respectively). Similar associations were observed between interoutcome interval and risk of low birthweight and preterm birth (pnon-linear  < 0.001). Moreover, interoutcome interval of ≥60 months was associated with an increased risk of cesarean delivery (pooled OR 1.72, 95% CI 1.04-2.83). For pregnancies following preterm births, an interpregnancy interval of 9 months was not associated with an increased risk of preterm birth, according to dose-response analyses (pnon-linear  = 0.008). Based on limited evidence, we did not observe significant associations between interpregnancy interval or interoutcome interval after pregnancy losses and risk of small for gestational age, fetal death, miscarriage, or preeclampsia (pooled OR range: 0.76-1.21; p > 0.05).

CONCLUSIONS

Extreme birth spacing has extensive adverse effects on maternal and infant health. In the general population, interpregnancy interval of 18-23 months may be associated with potential benefits for both mothers and infants. For women with previous preterm birth, the optimal birth spacing may be 9 months.

Short interpregnancy interval can lead to adverse pregnancy outcomes: A meta-analysis

BACKGROUND

The evidence of some previous papers was insufficient in studying the causal association between interpregnancy interval (IPI) and adverse pregnancy outcomes. In addition, more literature have been updated worldwide during the last 10 years.

METHODS

English and Chinese articles published from January 1980 to August 2021 in the databases of PubMed, Cochrane Library, Ovid, Embase, China Biology Medicine disc (CBM), and China National Knowledge Infrastructure (CNKI) were searched. Then following the inclusion and exclusion criteria, we screened the articles. Utilizing the Newcastle-Ottawa Scale (NOS), we evaluated the quality of the included articles. The literature information extraction table was set up in Excel, and the meta-analysis was performed with Stata 16.0 software (Texas, USA).

RESULTS

A total of 41 articles were included in the meta-analysis, and NOS scores were four to eight. The short IPI after delivery was the risk factor of preterm birth (pooled odds ratio 1.49, 95% confidence interval 1.42-1.57), very preterm birth (pooled OR: 1.82, 95% CI: 1.55-2.14), low birth weight (pooled OR: 1.33, 95% CI: 1.24-1.43), and small for gestational age (pooled OR: 1.14, 95% CI: 1.07-1.21), offspring death (pooled OR: 1.60, 95% CI: 1.51-1.69), NICU (pooled OR: 1.26, 95% CI: 1.01-1.57), and congenital abnormality (pooled OR: 1.10, 95% CI: 1.05-1.16), while was not the risk factor of gestational hypertension (pooled OR: 0.95, 95% CI: 0.93-0.98) or gestational diabetes (pooled OR: 1.06, 95% CI: 0.93-1.20).

CONCLUSION

Short IPI (IPI < 6 months) can lead to adverse perinatal outcomes, while it is not a risk factor for gestational diabetes and gestational hypertension. Therefore, more high-quality studies covering more comprehensive indicators of maternal and perinatal pregnancy outcomes are needed to ameliorate the pregnancy policy for women of childbearing age.

Interpregnancy interval after a miscarriage and obstetric outcomes in the subsequent pregnancy in a low-income setting, Nigeria: A cohort study

Objectives:

The aim of this study was to determine and compare the occurrence of adverse pregnancy outcomes in a cohort of pregnant women with interpregnancy interval of < and ⩾6 months (short and normal interpregnancy interval, respectively) following a spontaneous miscarriage in their last pregnancies.

Methods:

This was a cohort study that involved pregnant women with a spontaneous pregnancy loss in their last pregnancies. They were recruited at a gestational age of 13–15 weeks and followed up to determine the obstetric and foetal outcomes of their pregnancies at four tertiary hospitals in Nigeria from July 2018 to September 2019. Data collected were analysed using SPSS version 26.0. A Chi-square and multivariate logistic regression analysis were done, and a p-value of less than 0.05 was assumed to be statistically significant.

Results:

A total of 705 participants were studied, out of which 448 (63.5%) and 257 (36.5%) of the participants had short and normal interpregnancy interval after a spontaneous miscarriage. Over 80% of the participants had first-trimester pregnancy losses and were managed with manual vacuum aspiration in 73.3% of the cases. The majority, 87.5% for the normal interpregnancy interval cohort and 86.4% for the short interpregnancy interval cohort, had live births, while 8.5% and 10.1% of the women in the normal and short interpregnancy interval cohorts, respectively, had repeat miscarriages. There was no statistical difference in the occurrence of live births and repeat miscarriages between both cohorts (p > 0.05). There was no increased risk of occurrence of adverse foetomaternal outcomes in both groups (p > 0.05). Multivariate logistic regression analysis showed that there was no statistical difference in the occurrence adverse foetomaternal outcomes between the studied cohorts (p > 0.05).

Conclusion:

There was no significant difference in the occurrence of adverse maternal and foetal outcomes in the cohorts of mothers with short and normal interpregnancy interval following miscarriages in their last previous pregnancies.

The role of intervening pregnancy loss in the association between interpregnancy interval and adverse pregnancy outcomes

OBJECTIVE

To investigate whether intervening miscarriages and induced abortions impact the associations between interpregnancy interval after a live birth and adverse pregnancy outcomes.

DESIGN

Population-based cohort study.

SETTING

Norway.

PARTICIPANTS

A total of 165 617 births to 143 916 women between 2008 and 2016.

MAIN OUTCOME MEASURES

We estimated adjusted relative risks for adverse pregnancy outcomes using log-binomial regression, first ignoring miscarriages and induced abortions in the interpregnancy interval estimation (conventional interpregnancy interval estimates) and subsequently accounting for intervening miscarriages or induced abortions (correct interpregnancy interval estimates). We then calculated the ratio of the two relative risks (ratio of ratios, RoR) as a measure of the difference.

RESULTS

The proportion of short interpregnancy interval (<6 months) was 4.0% in the conventional interpregnancy interval estimate and slightly increased to 4.6% in the correct interpregnancy interval estimate. For interpregnancy interval <6 months, compared with 18-23 months, the RoR was 0.97 for preterm birth (PTB) (95% confidence interval [CI] 0.83-1.13), 0.97 for spontaneous PTB ( 95% CI 0.80-1.19), 1.00 for small-for-gestational age ( 95% CI 0.86-1.14), 1.00 for large-for-gestational age (95% CI 0.90-1.10) and 0.99 for pre-eclampsia (95% CI 0.71-1.37). Similarly, conventional and correct interpregnancy intervals yielded associations of similar magnitude between long interpregnancy interval (≥60 months) and the pregnancy outcomes evaluated.

CONCLUSION

Not considering intervening pregnancy loss due to miscarriages or induced abortions, results in negligible difference in the associations between short and long interpregnancy intervals and adverse pregnancy outcomes.

Interpregnancy interval and subsequent perinatal risk of congenital heart disease in Guangzhou, Southern China: a retrospective cohort study, 2014-2019

BACKGROUND

The association between maternal interpregnancy interval (IPI) and congenital heart disease (CHD) in neonates remains inconclusive. This study aimed to examine the effect of maternal IPI on birth risk of CHD.

METHODS

Chinese women with two consecutive singleton deliveries in Guangzhou between January 2014 and December 2019 were selected as participants. Information on IPI and CHD was extracted from the Guangzhou Perinatal Health Care and Delivery Registry and the Guangzhou Birth Defects Surveillance Program. We stratified IPI into four categories: <24 months, 24-35 months, 36-59 months, and ≥60 months. A multivariate logistic regression model was used to examine the association between IPI and CHD. Subgroup analysis was also performed to assess whether the associations differed across top three CHD subtypes.

RESULTS

For 119,510 women enrolled in this study, the mean ages at two consecutive deliveries were 26.2 ± 3.8 and 28.8 ± 4.0 years, which yielded a median IPI of 51.2 (interquartile range, 32.1-77.2) months. Among them, 828 delivered infants with CHD during their second pregnancy. There was a J-shaped curve relationship between IPI and CHD with the lowest birth prevalence (5.33‰) at 24-35-month interval. Compared to women with an IPI of 24-35 months, those with an IPI ≥60 had an increased risk of delivering infants with CHD (adjusted odds ratio (OR), 1.41; 95% confidence interval (CI), 1.19-1.64). However, for those with an IPI <24 months (adjusted OR, 1.24; 95% CI, 0.97-1.51), IPI was statistically insignificant associated with the risk of delivering infants with CHD (p = .12). There were different patterns of associations for different CHD subtypes.

CONCLUSIONS

Longer maternal IPI (≥60 months) was associated with an increased risk of delivering infants with CHD in the Chinese population.

Relationship between weight retention at 6 weeks postpartum and the risk of large-for-gestational age birth in a second pregnancy in China: a retrospective cohort study

OBJECTIVE

We aimed to investigate the association between weight retention at 6 weeks postpartum after the first pregnancy and large-for-gestational age (LGA) risk in a subsequent pregnancy.

STUDY DESIGN

A retrospective cohort study.

SETTING

A tertiary hospital of China.

PARTICIPANTS

5950 Chinese singleton pregnancies that delivered their second singletons between 28 and 42 weeks of gestation.

OUTCOMES MEASURES

We calculated the weight retention at 6 weeks postpartum after the first pregnancy (the body mass index (BMI) at 6 weeks after the first birth minus the prepregnant BMI of the first pregnancy) and the gestational weight gain in the second pregnancy. We used the logistic regression to obtain adjusted OR. We determined the relationship between maternal BMI change at 6 weeks after the first pregnancy and LGA risk in the second pregnancy.

RESULTS

Relative to other categories of BMI change at 6 weeks postpartum, women who gained ≥3 kg/m² compared with the prepregnancy BMI were at increased LGA risk. The stratified analysis showed that LGA risk was increased in the second pregnancy in underweight and normal weight women who gained ≥3 kg/m² when using remain stable women as the reference group (OR=3.35, 95% CI 1.11 to 10.12 for underweight women; OR=2.23, 95% CI 1.43 to 3.45 for normal weight women) at 6 weeks postpartum. For the women who gained ≥3 kg/m² at 6 weeks postpartum, LGA risk was increased in normal weight women with an adequate (OR=3.21, 95% CI 1.10 to 9.33) and excessive (OR=2.62, 95% CI 1.02 to 6.76) gestational weight in the second pregnancy when using obese women as the reference.

CONCLUSION

Postpartum weight retention at 6 weeks after the first pregnancy provides us a new early window to identify LGA risk in a subsequent pregnancy and allows us to implement primary preventative strategies.

Interpregnancy intervals and adverse birth outcomes in high-income countries: An international cohort study

BACKGROUND

Most evidence for interpregnancy interval (IPI) and adverse birth outcomes come from studies that are prone to incomplete control for confounders that vary between women. Comparing pregnancies to the same women can address this issue.

METHODS

We conducted an international longitudinal cohort study of 5,521,211 births to 3,849,193 women from Australia (1980-2016), Finland (1987-2017), Norway (1980-2016) and the United States (California) (1991-2012). IPI was calculated based on the time difference between two dates-the date of birth of the first pregnancy and the date of conception of the next (index) pregnancy. We estimated associations between IPI and preterm birth (PTB), spontaneous PTB, and small-for-gestational age births (SGA) using logistic regression (between-women analyses). We also used conditional logistic regression comparing IPIs and birth outcomes in the same women (within-women analyses). Random effects meta-analysis was used to calculate pooled adjusted odds ratios (aOR).

RESULTS

Compared to an IPI of 18-23 months, there was insufficient evidence for an association between IPI <6 months and overall PTB (aOR 1.08, 95% CI 0.99-1.18) and SGA (aOR 0.99, 95% CI 0.81-1.19), but increased odds of spontaneous PTB (aOR 1.38, 95% CI 1.21-1.57) in the within-women analysis. We observed elevated odds of all birth outcomes associated with IPI ≥60 months. In comparison, between-women analyses showed elevated odds of adverse birth outcomes for <12 month and >24 month IPIs.

CONCLUSIONS

We found consistently elevated odds of adverse birth outcomes following long IPIs. IPI shorter than 6 months were associated with elevated risk of spontaneous PTB, but there was insufficient evidence for increased risk of other adverse birth outcomes. Current recommendations of waiting at least 24 months to conceive after a previous pregnancy, may be unnecessarily long in high-income countries.

Association between interpregnancy interval and hypertensive disorders of pregnancy: Effect modification by maternal age

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.

Macrosomia and large for gestational age in Asia: One size does not fit all

Macrosomia, usually defined as infant birth weight of ≥4000 g, does not consider gestational age, sex, or country/region-specific differences in mean birth weight and maternal body weight. This issue is particularly relevant for Asia, where 60% of the world's population lives, due to variations in maternal size and birth weights across populations. Large for gestational age (LGA), defined as birth weight > 90th centile, is a more sensitive measure as it considers gestational age and sex, though it is dependent on the choice of growth charts. We aimed to review reporting of macrosomia and LGA in Asia. We reviewed the literature on prevalence and risk of macrosomia and LGA in Asia over the last 29 years. Prevalence of macrosomia ranged from 0.5% (India) to 13.9% (China) while prevalence of LGA ranged from 4.3% (Korea) to 22.1% (China), indicating substantial variation in prevalence within and between Asian countries. High pre-pregnancy body mass index, excessive gestational weight gain, and impaired glucose tolerance conferred risk of macrosomia/LGA. Incidence of macrosomia and LGA varies substantially within and between Asian countries, as do the growth charts and definitions. The latter makes it impossible to make comparisons but suggests differences in intrauterine growth between populations. Reporting LGA, using standardized country/regional growth charts, would better capture the incidence of high birth weight and allow for comparison and identification of contributing factors. Better understanding of local drivers of excessive intrauterine growth could enable development of improved strategies for prevention and management of LGA.

Short and long interpregnancy interval and the risk for pediatric obstructive sleep apnea in the offspring

INTRODUCTION

Interpregnancy interval (IPI) is defined as the period between a live birth and the conception of a subsequent fetus. Both short (IPI < 6 months) and long IPI (IPI > 60 months) have been shown to increase the risk for adverse perinatal outcomes, some of which, are known risk factors for obstructive sleep apnea syndrome (OSAS) in the offspring.

AIMS

To study the association between IPI and risk for offspring OSAS, during a follow-up period of up to 18 years.

STUDY DESIGN

Population-based cohort.

SUBJECTS

In this population-based cohort analysis, all singleton live births, born to a mother with at least one previous birth occurring between 1991 and 2014, were included. Congenital malformations were excluded.

MATERIALS AND METHODS

Hospitalizations of the offspring due to OSAS diagnosis up to 18 years of age, were evaluated according to IPI length. Intermediate IPI (6-60 months) was considered as the reference. A Kaplan-Meier survival curve and a Cox hazards regression model were used to compare the incidence of OSAS between the groups, and to adjust for confounding variables.

RESULTS

The study population included 144,397 deliveries, of which 13.1% (n = 18,947) were followed by short IPI, 7.9% (n = 11,438) and 79.0% (n = 114,012) were followed by long and intermediate IPI, respectively. OSAS hospitalization rates were significantly higher among the long IPI group compared to intermediate and short IPIs (0.9%; 0.7% and 0.6%, respectively, p = .001). The association between long IPI and offspring pediatric OSAS remained significant after controlling for preterm delivery, maternal diabetes, and smoking, and mode of delivery, (adjusted HR = 1.45; 95% CI, 1.17-1.80).

CONCLUSIONS

Children born following long IPI are at increased risk for pediatric OSAS.

Use of E-values for addressing confounding in observational studies-an empirical assessment of the literature

BACKGROUND

E-values are a recently introduced approach to evaluate confounding in observational studies. We aimed to empirically assess the current use of E-values in published literature.

METHODS

We conducted a systematic literature search for all publications, published up till the end of 2018, which cited at least one of two inceptive E-value papers and presented E-values for original data. For these case publications we identified control publications, matched by journal and issue, where the authors had not calculated E-values.

RESULTS

In total, 87 papers presented 516 E-values. Of the 87 papers, 14 concluded that residual confounding likely threatens at least some of the main conclusions. Seven of these 14 named potential uncontrolled confounders. 19 of 87 papers related E-value magnitudes to expected strengths of field-specific confounders. The median E-value was 1.88, 1.82, and 2.02 for the 43, 348, and 125 E-values where confounding was felt likely to affect the results, unlikely to affect the results, or not commented upon, respectively. The 69 case-control publication pairs dealt with effect sizes of similar magnitude. Of 69 control publications, 52 did not comment on unmeasured confounding and 44/69 case publications concluded that confounding was unlikely to affect study conclusions.

CONCLUSIONS

Few papers using E-values conclude that confounding threatens their results, and their E-values overlap in magnitude with those of papers acknowledging susceptibility to confounding. Facile automation in calculating E-values may compound the already poor handling of confounding. E-values should not be a substitute for careful consideration of potential sources of unmeasured confounding. If used, they should be interpreted in the context of expected confounding in specific fields.

Association between exposure during pregnancy and the risk of developing solid tumors in second children: Results from a Chinese matched case-control study

BACKGROUND

Even though many studies have proven the risk factors for cancer in children, studies focusing exclusively on second children are absent. This study is designed to examine the association between maternal exposure during pregnancy and the risk of developing solid tumors (STs) in second children.

METHODS

This retrospective matched case-control study included 80 s children with STs and 160 s children without STs matched in terms of birth weight, gestational age, pregnancy body mass index (BMI), and residence from a medical center. Exposure during pregnancy and birth characteristics of these children were investigated through structured questionnaires.

RESULTS

A univariate analysis suggested that birth spacing (OR, 12.70; CI, 4.44-36.34), maternal smoking (OR, 6.00; CI, 1.62-22.16), paternal smoking (OR, 2.20; CI, 1.23-3.93), and common cold (OR,1.94; CI, 1.02-3.69) were associated with an increased risk of second children STs. A multivariate analysis demonstrated that birth spacing (OR, 12.45; CI, 4.00-38.78) and paternal smoking (OR, 2.04; CI, 1.04-3.99) were the main risk factors for STs in second-born children.

CONCLUSION

Long birth spacing (>10 years) and paternal smoking could significantly increase the risk of developing STs in second-born children. Despite the fact that the effects of maternal smoking and the common cold were not significant, it is still recommended to quit smoking, take necessary self-protective measures to reduce the risk of infection.

Interpregnancy interval and risk of perinatal death: a systematic review and meta-analysis

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.

Interpregnancy intervals and women's knowledge of the ideal timing between birth and conception

BACKGROUND

Short interpregnancy intervals (IPIs) are associated with adverse obstetric outcomes. However, few studies have explored women's understanding of ideal IPIs or investigated knowledge of the consequences of short IPIs.

METHODS

We performed a prospective questionnaire-based study at two hospitals in Sydney, Australia. We recruited women attending antenatal clinics and collected demographic data, actual IPI, ideal IPI, contraceptive use, and education provided on birth-spacing and contraception following a previous live birth. We explored associations between an IPI <12 months and a selection of demographic and health variables.

RESULTS

Data were collected from 467 women, of whom 344 were pregnant following a live birth. Overall, 72 (20.9%) women had an IPI <12 months only 7.5% of whom believed this was ideal, and the remaining stating their ideal IPI was over 12 months (52.3%) or they had no ideal IPI (40.3%). IPI <12 months following a live birth was significantly associated with younger age (p=0.043) but not with ethnicity, relationship status, education, religion, parity nor previous mode of delivery. IPI <12 months was associated with non-use of long-acting reversible contraception (LARC) (p<0.001), breastfeeding <12 months (p=0.041) and shorter ideal IPI (p=0.03). Less than half of the women (43.3%, n=149) reported having received advice about IPI and less than half about postnatal contraception (44.2%, n=147).

CONCLUSIONS

Younger age and non-use of LARC are significantly associated with IPIs <12 months. A minority of women with a short IPI perceived it to be ideal. Prevention of short IPIs could be achieved with improved access to postnatal contraception.

The mnemonic code of pregnancy: Comparative analyses of pregnancy success and complication risk in first and second human pregnancies

Obstetrical complications such as spontaneous abortion/miscarriage, fetal growth restriction, preeclampsia or preterm birth occur in approx. 15% of human pregnancies. Clinical experts often state that a previous uncomplicated pregnancy reduces the risk for complications in subsequent pregnancies. Vice versa, a prior pregnancy affected by obstetrical complications increases the risk for reoccurrence. However, published evidence directly underpinning these clinical statements is sparse. Considering that the maternal immune adaptation may be causally involved in determining the outcome of subsequent pregnancies, a comprehensive analysis of clinical data was long overdue. We here present a systematic analysis of clinical data using a PubMed-based approach to identify human studies with relevant information on birth weight and incidences of pregnancy complications in first and second pregnancies. From initially 18,592 publications, 37 studies were included in the quantitative data analysis. Women with a previous pregnancy affected by complications where a derailed immune response can be inferred have a 2.2-3.2-fold increased risk to be affected again in a subsequent pregnancy. Conversely, a normally progressing primary pregnancy reduced the risk for complications in a subsequent pregnancy by 35-65%. Moreover, an uncomplicated primary pregnancy was associated with a 4.2% increased birth weight in a following pregnancy without a difference in gestational age at delivery. In conclusion, the increased birth weight after previously uncomplicated pregnancies suggests that an immune memory is mounted during primary pregnancies. This immune memory may promote the successful outcome of subsequent pregnancies or - if missing or compromised - account for a risk perpetuation of pregnancy complications.

Association of Short Interpregnancy Interval With Pregnancy Outcomes According to Maternal Age

IMPORTANCE

Interpregnancy intervals shorter than 18 months are associated with higher risks of adverse pregnancy outcomes. It is currently unknown whether short intervals are associated with increased risks among older women to the same extent as among younger women.

OBJECTIVE

To evaluate whether the association between short interpregnancy (delivery to conception) interval and adverse pregnancy outcomes is modified by maternal age.

DESIGN, SETTING, AND PARTICIPANTS

A population-based cohort study conducted in British Columbia, Canada, evaluated women with 2 or more singleton pregnancies from 2004 to 2014 with the first (index) pregnancy resulting in a live birth. Data analysis was performed from January 1 to July 20, 2018.

MAIN OUTCOMES AND MEASURES

Risks of maternal mortality or severe morbidity (eg, mechanical ventilation, blood transfusion >3 U, intensive care unit admission, organ failure, death), small-for-gestational age (<10th birthweight percentile for gestational age and sex), fetal and infant composite outcome (stillbirth, infant death, <third birthweight percentile for gestational age and sex, delivery <28 weeks), and spontaneous and indicated preterm delivery. Risks of each outcome for 3- to 24-month interpregnancy intervals were estimated, according to maternal age at index birth (20-34 and ≥35 years). Adjusted risk ratios (aRRs) comparing predicted risks at 3-, 6-, 9-, and 12-month intervals with risks at 18-month intervals for each age group were calculated. The potential role of other factors explaining any differences (unmeasured confounding) was examined in several sensitivity analyses.

RESULTS

Among 148 544 pregnancies, maternal mortality or severe morbidity risks were increased at 6-month compared with 18-month interpregnancy intervals for women aged 35 years or older (0.62% at 6 months vs 0.26% at 18 months; aRR, 2.39; 95% CI, 2.03-2.80), but not for women aged 20 to 34 years (0.23% at 6 months vs 0.25% at 18 months; aRR, 0.92; 95% CI, 0.83-1.02). Increased adverse fetal and infant outcome risks were more pronounced for women aged 20 to 34 years (2.0% at 6 months vs 1.4% at 18 months; aRR, 1.42; 95% CI, 1.36-1.47) than women 35 years or older (2.1% at 6 months vs 1.8% at 18 months; aRR, 1.15; 95% CI, 1.01-1.31). Risks of spontaneous preterm delivery at 6-month interpregnancy intervals were increased for women 20 to 34 years old (5.3% at 6 months vs 3.2% at 18 months; aRR, 1.65; 95% CI, 1.62-1.68) and to a lesser extent for women 35 years or older (5.0% at 6 months vs 3.6% at 18 months; aRR, 1.40; 95% CI, 1.31-1.49). Modest increases in risks of small-for-gestational age and indicated preterm delivery at short intervals did not vary meaningfully by maternal age. Sensitivity analyses suggested that observed associations were not fully explained by unmeasured confounding.

CONCLUSIONS AND RELEVANCE

The findings of this study suggest that short interpregnancy intervals are associated with increased risks for adverse pregnancy outcomes for women of all ages.