Inter-Pregnancy Intervals and the Risk of Autism Spectrum Disorder: Results of a Population-Based Study.
Both very short and very long gaps between pregnancies double the chance of autism in the second child.
01Research in Context
What this study did
Researchers looked at 283,000 Wisconsin birth records. They asked: does the time between pregnancies change the chance the second child gets an autism diagnosis?
They split the gaps into five groups: under 12 months, 12-23, 24-47, 48-84, and over the study period. The 24-47 month group was the baseline.
What they found
Very short gaps (under 12 months) doubled the odds of ASD. Very long gaps (over the study period) also doubled the odds.
The safest window was 24-47 months. Gaps of 12-23 or 48-84 months showed no clear extra risk.
How this fits with other research
Fairthorne et al. (2016) found that moms with a history of mental-health visits also double the odds of ASD in later kids. Both papers point to pre-conception factors you can ask about on day one.
Lyall et al. (2011) showed early menarche and high teen BMI raise risk slightly. Their effect sizes are smaller than the spacing effect seen here, so birth spacing may be the stronger signal.
Brayette et al. (2019) found that preterm birth lowers cognitive scores in kids who already have ASD. Nickerson et al. (2015) did not look at gestational age, so the two risks could stack—close spacing plus prematurity might be extra tough.
Why it matters
When you take a developmental history, ask about the gap between the client and the next-oldest sibling. If it is under one year or over seven years, flag the chart for closer developmental monitoring and earlier screening. You cannot change birth spacing after the fact, but you can use the info to push for timely evaluations and extra parent coaching.
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02At a glance
03Original 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.
Journal of autism and developmental disorders, 2015 · doi:10.1007/s10803-015-2368-y