Inter-Pregnancy Intervals and the Risk of Autism Spectrum Disorder: Results of a Population-Based Study

Abstract

Recent studies have reported an increased risk of autism among second-born children conceived <12 versus >36 months after the birth of a sibling. Confirmation of this finding would point to inter-pregnancy interval (IPI) as a potentially modifiable risk factor for autism. This study evaluated the relationship between IPI and autism spectrum disorder (ASD) risk in a Wisconsin birth cohort of 31,467 second-born children, of whom 160 resided in the study area and were found to have ASD at age 8 years. In adjusted analyses, both short (<12) and long (>84 month) IPIs were associated with a two-fold risk of ASD relative to IPIs of 24-47 months (p<0.05). The long IPI association was partially confounded by history of previous pregnancy loss.

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

“…32 However, a sensitivity analysis restricted to individuals with more severe ASD revealed a significant association between IPIs of <12 months and this disorder. Three studies also found a significant association between ASD and long IPIs (≥60 months, 31 ≥72 months, 34 and ≥84 months 33 ). Five studies reported a significantly increased risk of the former subtype autistic disorder associated with short IPIs.…”

“…Five studies reported a significantly increased risk of the former subtype autistic disorder associated with short IPIs. 28,30,31,33,34 No relationship was found between long IPIs and this disorder in 3 studies. 28,31,33 However, long IPIs were found to be associated with an increased risk of the former subtypes Asperger disorder and PDD-NOS in 3 studies.…”

“…28,30,31,33,34 No relationship was found between long IPIs and this disorder in 3 studies. 28,31,33 However, long IPIs were found to be associated with an increased risk of the former subtypes Asperger disorder and PDD-NOS in 3 studies. 31,33,34 Overall, there was no association between short IPIs and the risk of these 2 disorders.…”

“…A total of 12 studies (6 cohort, 5 cross-sectional, and 1 case-control), including 1 334 569 children, met the inclusion criteria. [28][29][30][31][32][33][34][35][36][37][38][39] The individual characteristics and main findings of the studies included in the systematic review are shown in Table 1. Seven studies provided data on ASD, 28 …”

“…[28][29][30][31][32][33][34] Three studies showed a U-shaped association between IPI and the risk of ASD. 31,33,34 Six studies found a significant association between short IPIs (<12 months, 30,31,33 <18 months, 29 <24 months, 34 and <36 months 28 ) and increased risk of ASD. The remaining study reported a nonsignificant greater risk of ASD among children born after an IPI of <12 months (adjusted OR 1.72, 95% CI 0.96-3.06).…”