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A large body of research has found an association between short birth intervals and the risk of infant mortality in developing countries, but recent work on other perinatal outcomes from highly developed countries has called these claims into question, arguing that previous studies have failed to adequately control for unobserved heterogeneity. Our study addresses this issue by estimating within-family models on a sample of 4.5 million births from 77 countries at various levels of development. We show that after unobserved maternal heterogeneity is controlled for, intervals shorter than 36 months substantially increase the probability of infant death. However, the importance of birth intervals as a determinant of infant mortality varies inversely with maternal education and the strength of the relationship varies regionally. Finally, we demonstrate that the mortality-reducing effects of longer birth intervals are strong at low levels of development but decline steadily toward zero at higher levels of development. These findings offer a clear way to reconcile previous research showing that birth intervals are important for perinatal outcomes in lowincome countries but are much less consequential in high-income settings.

Short inter-pregnancy interval is an interval of <24 months between the dates of birth of the preceding child and the conception date of the current pregnancy. Despite its direct effects on the perinatal and maternal outcomes, there is a paucity of evidence on its prevalence and determinant factors, particularly in Ethiopia. Therefore, this study assessed the prevalence and associated factors of short inter-pregnancy interval among pregnant women in Debre Berhan town, Northern Ethiopia. A community based cross-sectional study was conducted among a randomly selected 496 pregnant women in Debre Berhan town from February 9 to March 9, 2020. The data were collected by using an interviewer-administered questionnaire and analyzed using STATA (14.2) statistical software. To identify the predictors of short inter-pregnancy interval, multivariable binary logistic regression was fitted and findings are presented using adjusted odds ratio (AOR) with 95% confidence interval (CI). The overall prevalence of short inter-pregnancy interval (<24 months) among pregnant women was 205 (40.9%). Being over 30 years of age at first birth (AOR = 3.50; 95% CI: 2.12-6.01), non-use of modern contraceptive (AOR = 2.51; 95% CI: 1.23-3.71), duration of breastfeeding for less than 12 months (AOR = 2.62; 95% CI: 1.32-5.23), parity above four (AOR = 0.31; 95% CI: 0.05-0.81), and unintended pregnancy (AOR = 5.42; 95% CI: 3.34-9.22) were independently associated factors with short inter-pregnancy interval. Despite the public health interventions being tried in the country, the prevalence of short inter-pregnancy interval in this study is high. Therefore, it implies that increasing contraceptive use and encouraging optimal breastfeeding might help in the efforts made to avert the problem.

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. In this systematic review and meta‐analysis of 129 studies, extreme short or long birth spacing was associated with increased odds of adverse pregnancy and birth outcomes. In the general population, interpregnancy interval of 18 to 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.

Introduction Short inter-birth intervals negatively impact maternal and child health; however, data on their prevalence and associated factors in Tanzania are limited. This study investigates the prevalence of short inter-birth intervals and the associated factors among women of reproductive age in Tanzania. Methods This was a cross-sectional study utilizing the 2022 Tanzania Demographic and Health Survey and Malaria Indicator Survey dataset. The study population included women aged 15–49 years with at least two births within five years preceding the survey. A short inter-birth interval was defined as a birth occurring < 33 months after the preceding birth. A generalized linear model with Poisson as a link and robust standard errors was used to examine factors associated with short inter-birth intervals. A p -value < 0.05 was considered statistically significant. Results A total of 8,350 births from 6,034 women were included in this analysis. The mean (± SD) age of the women was 31.6 ± 6.8 years. The overall prevalence of short inter-birth intervals was 42.6%. Younger age (aPR 3.12, 95% CI 2.88–3.52 for age 15–24 years, and aPR 1.74, 95% CI 1.62–1.1.86 for age 25–34 years), being married (aPR 1.27, 95% CI 1.03–1.57), late age at first childbirth (aPR 1.24, 95% CI 1.17–1.32) for a 20–24 years and aPR 1.55, 95% CI 1.39–1.73 for ≥ 25 years), and higher birth order (aPR 1.02, 95% CI 1.03–1.19; aPR 1.24, 95% CI 1.14–1.34; aPR 1.72, 95% CI 1.58–1.86 for 3rd, 4th, and 5th or more birth orders, respectively, compared to 2nd birth order) were independently associated with short inter-birth intervals. Additionally, there was significant variation in the prevalence of short inter-birth intervals across different zones and levels of household wealth. Women from richer (aPR 0.87, 95% CI: 0.80–0.95) and richest (aPR 0.84, 95% CI: 0.74–0.94) households exhibited a lower prevalence of short inter-birth intervals. Conclusion This study highlights the significant prevalence of short inter-birth intervals among women of reproductive age in Tanzania. The associated factors include younger age, marital status, delayed first childbirth, higher birth order, geographical disparities, and lower household wealth. These findings highlight the need for targeted interventions to promote birth spacing and improve maternal and child health outcomes.

Background Research has shown a relationship between interpregnancy intervals (IPIs) and preterm birth, but a comprehensive understanding remains elusive. The aim of this systematic review and meta-analysis was to examine the effect of different IPIs on the risk of preterm birth Methods Systematic searches were conducted in PubMed, Cochrane, Web of Science, and Embase up to June 2, 2023. Studies included in the review provided data on IPIs and preterm birth outcomes, assessed via the NOS quality scale. A Bayesian network meta-analysis was performed to evaluate the association between IPIs and preterm birth. Results From 34 studies and 8,646,679 individuals, the optimal IPIs were found to be 24-29 months, showing significantly lower risks of preterm birth at less than 32 weeks of gestation [OR=0.55 (95%CI: 0.50 - 0.62)]and at less than 37 weeks of gestation[OR=0.61 (95%CI: 0.59 - 0.63)]compared to IPIs less than 5 months. Conclusions IPIs of 24-29 months significantly reduce the risk of preterm birth, suggesting a potential target range for family planning and clinical recommendations. Trial registration Not applicable.

A growing body of research has argued that the traditional categories of stopping and spacing are insufficient to understand why individuals want to control fertility. In a series of articles, Timæus, Moultrie, and colleagues defined a third type of fertility motivation—postponement—that reflects a desire to avoid childbearing in the short term without clear goals for long-term fertility. Although postponement is fundamentally a description of fertility desires, existing quantitative research has primarily studied fertility behavior in an effort to find evidence for the model. In this study, we use longitudinal survey data to consider whether postponement can be identified in standard measures of fertility desires among reproductive-age women in rural Mozambique. Findings show strong evidence for a postponement mindset in this population, but postponement coexists with stopping and spacing goals. We reflect on the difference between birth spacing and postponement and consider whether and how postponement is a distinctive sub-Saharan phenomenon.

Short birth interval (SBI), defined as < 33 months between two consecutive live births, remains a pressing public health concern in Nigeria, with potential adverse consequences for both mothers and children. Understanding the factors associated with SBI is crucial for developing effective interventions to improve maternal and child health outcomes. This study investigates the sociodemographic and regional disparities influencing SBI among women of reproductive age in Nigeria, utilizing data from the 2018 Nigeria Demographic and Health Survey (NDHS). This study analysed data from 25,280 women of reproductive age who had given birth within five years preceding the NDHS survey. Bivariate and multivariable logistic regression analyses were conducted to assess the relationship between SBI and associated factors. Prevalence rates were analysed and presented using map and chart to highlight regional disparities. The overall prevalence of SBI in Nigeria was 51.6%. Older age was associated with a higher likelihood of optimal birth interval (AOR = 3.23, 95% confidence interval [CI]: 2.32–4.50, p  < 0.001). Women in the South East (55.3%) and North West (52.2%) regions had the highest prevalence of SBI, while the South West had the lowest (38.4%). South East had lower odds of optimal BI (AOR = 0.67, 95% CI: 0.59–0.75, p  < 0.001) compared to the North Central region. Higher education (AOR = 0.85, 95% CI: 0.74–0.99, p  = 0.03) was associated with reduced odds of SBI, but wealth index did not show significant associations in the adjusted analysis. This study highlights significant regional disparities in short birth interval SBI in Nigeria. Interventions addressing regional and educational disparities, particularly in underserved regions, are essential for promoting optimal birth intervals and improving maternal and child health outcomes.

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 (PM 2.5 ), PM 10 , ozone (O 3 ), nitrogen dioxide (NO 2 ), sulfur dioxide (SO 2 ) 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 PM 2.5 , PM 10 , O 3 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 PM 2.5 was noted during the first trimester. Compared to records with normal IPI and low PM 2.5 exposure, those with short IPI and high PM 2.5 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.

Background Few studies have investigated the predictors of short and long interpregnancy intervals in Japan. Thus, this study investigated the maternal sociodemographic characteristics of short and long interpregnancy intervals among multiparous women using nationwide data in Japan. Methods The data of the Longitudinal Survey of Newborns in the 21st Century (2010 Cohort) in Japan were used, and the interpregnancy intervals of mothers were calculated. The age group, marital status, number of births, employment status, educational attainment of mothers, and household income were used as explanatory variables. Interpregnancy intervals of less than 12 months and 60 months or more were defined as short and long interpregnancy intervals, respectively. A modified Poisson regression model was employed to investigate the relationships between short and long interpregnancy intervals and maternal characteristics, and unadjusted and adjusted analyses were conducted. Results A total of 19,879 infants were used in the analysis. The results of the adjusted regression analysis showed that the risk ratio for short interpregnancy intervals increased with a decrease in maternal age, whereas the opposite trend was observed for long interpregnancy intervals. In addition, low educational attainment was positively associated with long interpregnancy intervals, and low household income was positively associated with short interpregnancy intervals. Employment status also played a role, with working mothers showing a negative association with short interpregnancy intervals and a positive association with long interpregnancy intervals. Conclusions This study showed that maternal sociodemographic characteristics such as employment status, educational attainment, and household income were associated with short and long interpregnancy intervals in Japan.

We use duration models on a well-known historical data set of more than 15,000 families and 60,000 births in England for the period 1540-1850 to show that the sampled families adjusted the timing of their births in accordance with the economic conditions as well as their stock of dependent children. The effects were larger among the lower socioeconomic ranks. Our findings on the existence of parity-dependent as well as parity-independent birth spacing in England are consistent with the growing evidence that marital birth control was present in pre-transitional populations.