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.