Birth Spacing and Risk of Autism and Other Neurodevelopmental Disabilities: A Systematic Review.

CONTEXT: Both short and long interpregnancy intervals (IPIs) have recently been associated with increased risk of autism spectrum disorder (ASD). However, this association has not been systematically evaluated. OBJECTIVE: To examine the relationship between birth spacing and the risk of ASD and other neurodevelopmental disabilities. DATA SOURCES: Electronic databases from their inception to December 2015, bibliographies, and conference proceedings. STUDY SELECTION: Observational studies with results adjusted for potential confounding factors that reported on the association between IPIs or birth intervals and neurodevelopmental disabilities. DATA EXTRACTION: Two reviewers independently extracted data on study characteristics, IPIs/birth intervals, and outcome measures. RESULTS: Seven studies (1 140 210 children) reported an association between short IPIs and increased risk of ASD, mainly the former subtype autistic disorder. Compared with children born to women with IPIs of ≥36 months, children born to women with IPIs of <12 months had a significantly increased risk of any ASD (pooled adjusted odds ratio [OR] 1.90, 95% confidence interval [CI] 1.16-3.09). This association was stronger for autistic disorder (pooled adjusted OR 2.62, 95% CI 1.53-4.50). Three of these studies also reported a significant association between long IPIs and increased risk of ASD. Short intervals were associated with a significantly increased risk of developmental delay (3 studies; 174 940 children) and cerebral palsy (2 studies; 19 419 children). LIMITATIONS: Substantial heterogeneity, and few studies assessing neurodevelopmental disabilities other than ASD. CONCLUSIONS: Short IPIs are associated with a significantly increased risk of ASD. Long IPIs also appear to increase the risk of ASD.

Effects of birth spacing on maternal, perinatal, infant, and child health: a systematic review of causal mechanisms.

This systematic review of 58 observational studies identified hypothetical causal mechanisms explaining the effects of short and long intervals between pregnancies on maternal, perinatal, infant, and child health, and critically examined the scientific evidence for each causal mechanism hypothesized. The following hypothetical causal mechanisms for explaining the association between short intervals and adverse outcomes were identified: maternal nutritional depletion, folate depletion, cervical insufficiency, vertical transmission of infections, suboptimal lactation related to breastfeeding-pregnancy overlap, sibling competition, transmission of infectious diseases among siblings, incomplete healing of uterine scar from previous cesarean delivery, and abnormal remodeling of endometrial blood vessels. Women's physiological regression is the only hypothetical causal mechanism that has been proposed to explain the association between long intervals and adverse outcomes. We found growing evidence supporting most of these hypotheses.

Effect of the interpregnancy interval on perinatal outcomes in Latin America.

OBJECTIVE: To estimate whether interpregnancy interval is independently associated with increased risk of perinatal death and other adverse perinatal outcomes. METHODS: We investigated the effect of interpregnancy interval on perinatal outcomes in 1,125,430 pregnancies recorded in the Perinatal Information System database of the Latin American Center for Perinatology and Human Development, Montevideo, Uruguay, between 1985 and 2004. Odds ratios (ORs) were adjusted for 16 major confounding factors using multiple logistic regression models. RESULTS: Compared with infants with interpregnancy intervals of 18-23 months, those born to women with intervals shorter than 6 months had an increased risk of early neonatal death (adjusted OR 1.49, 95% confidence interval [CI] 1.06-1.96), fetal death (adjusted OR 1.54, 95% CI 1.28-1.83), low birth weight (adjusted OR 1.88, 95% CI 1.78-1.90), very low birth weight (adjusted OR 2.01, 95% CI 1.73-2.31), preterm birth (adjusted OR 1.80, 95% CI 1.71-1.89), very preterm birth (adjusted OR 1.95, 95% CI 1.67-2.26), and small for gestational age (adjusted OR 1.30, 95% CI 1.25-1.36). Intervals of 6-11 months and 60 months and longer were also associated with a significantly greater risk for the 7 adverse perinatal outcomes. CONCLUSION: In Latin America, interpregnancy intervals shorter than 12 months and longer than 59 months are independently associated with increased risk of adverse perinatal outcomes. These data suggest that spacing pregnancies appropriately could prevent perinatal deaths and other adverse perinatal outcomes in the developing world.