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

UNASSIGNED: This study aimed to systematically review the literature on the associations between birth spacing and developmental outcomes in early childhood (3-10 years of age). Studies examining the associations between interpregnancy intervals and child development outcomes during and beyond the perinatal period have not been systematically reviewed.
UNASSIGNED: We searched Ovid/MEDLINE, Global Health, PsycINFO, EMBASE, CINAHL Plus, Educational Source, Research Starters, ERIC, Scopus, PubMed, Social Science Research Network database, and ProQuest\'s Social Sciences Databases for relevant articles published between 1 January 1989 and 25 June 2021. Studies published in English, conducted in populations residing in high-income countries with any measure of birth spacing, and child development outcomes among children aged <10 years were included. Two authors independently assessed the eligibility of studies and extracted data on the study design, setting and population, birth spacing, outcomes, and results.
UNASSIGNED: The search yielded 1,556 records, of which seven studies met the inclusion criteria. Five of these seven studies used birth intervals as the exposure measure. Definitions of exposure differed between the studies. Three studies reported an association between short birth spacing and poorer child development outcomes, and two studies reported an association between long birth spacing and poorer child development outcomes.
UNASSIGNED: Currently, limited evidence suggests that the adverse effects of sub-optimal birth spacing are observable beyond infancy.

Women in high resource nations are increasingly delaying childbearing until their thirties. Delayed childbearing poses challenges for the spacing of a woman\'s pregnancies. Inter-pregnancy intervals <12 months are associated with risk for adverse pregnancy outcome, yet increased maternal age at delivery is linked with increased risk. The optimal inter-pregnancy interval for older mothers is uncertain. This systematic review will aim to assess the relation between inter-pregnancy interval and perinatal and maternal health outcomes in women who delay childbearing to age 30 and older.
We will search MEDLINE, CINAHL, and EMBASE databases for peer-reviewed articles on the effects of inter-pregnancy interval on perinatal and maternal health outcomes among women over 29 years at the time of first birth, in high-income countries. To assess the quality of studies, the Cochrane\'s Collaboration tool for assessing risk of bias will be used for randomized controlled trials, and the Newcastle-Ottawa tool to assess quality of case control and cross-sectional studies. The quality of the findings on each outcome will be assessed across studies, using the GRADE approach. The decision to conduct meta-analyses will be based on the concordance in definitions used for inter-pregnancy intervals, age groups studied, or outcomes measured among selected studies. We will report odds ratios and/or relative risks and/or risk differences for different inter-pregnancy intervals and perinatal and maternal outcomes as well as pregnancy complications.
This systematic review will summarize existing data on the relation between inter-pregnancy interval and perinatal and maternal health outcomes among women who delay childbearing to age 30 and older. Findings will inform clinical best practices to assist mothers over age 30 to space their pregnancies appropriately.
Prospero CRD42015019057.

BACKGROUND: Women with a history of pre-eclampsia have a higher risk of developing pre-eclampsia in subsequent pregnancies. However, the role of the inter-pregnancy interval on this association is unclear.
OBJECTIVE: To explore the effect of inter-pregnancy interval on the risk of recurrent pre-eclampsia or eclampia.
METHODS: MEDLINE, EMBASE and LILACS were searched (inception to July 2015).
METHODS: Cohort studies assessing the risk of recurrent pre-eclampsia in the immediate subsequent pregnancy according to different birth intervals.
METHODS: Two reviewers independently performed screening, data extraction, methodological and quality assessment. Meta-analysis of adjusted odds ratios (aOR) with 95 % confidence intervals (CI) was used to measure the association between various interval lengths and recurrent pre-eclampsia or eclampsia.
RESULTS: We identified 1769 articles and finally included four studies with a total of 77,561 women. The meta-analysis of two studies showed that compared to inter-pregnancy intervals of 2-4 years, the aOR for recurrent pre-eclampsia was 1.01 [95 % CI 0.95 to 1.07, I(2) 0 %] with intervals of less than 2 years and 1.10 [95 % CI 1.02 to 1.19, I(2) 0 %] with intervals longer than 4 years.
CONCLUSIONS: Compared to inter-pregnancy intervals of 2 to 4 years, shorter intervals are not associated with an increased risk of recurrent pre-eclampsia but longer intervals appear to increase the risk. The results of this review should be interpreted with caution as included studies are observational and thus subject to possible confounding factors.