(HealthDay News) — Risk of autism spectrum disorder (ASD) may be higher in children born after interpregnancy intervals of less than two years or greater than six years, according to a study published online September 14 in Pediatrics.

Ousseny Zerbo, PhD, from Kaiser Permanente Northern California (KPNC) in Oakland, and colleagues evaluated medical records data from a cohort of 45,261 children born at KPNC between 2000–2009 to determine the association between interpregnancy interval and ASD risk in second-born children.

The researchers found that children born after an interpregnancy interval of <12 months or ≥72 months had a two- to threefold increased risk of ASD compared with children born after an interval of 36–47 months. Adjusted hazard ratios (95% confidence intervals) were 3 (1.9-4.7) for an interpregnancy interval of less than six months, 2.1 (1.4-3.3) for an interpregnancy interval of six to eight months, 1.9 (1.3-2.1) for an interpregnancy interval of nine to 11 months, 1.5 (1.1-2.1) for an interpregnancy interval of 12–23 months and 2.4 (1.5-3.7) for an interpregnancy interval of at least 72 months. Maternal BMI, change in BMI between pregnancies, parental age, maternal antidepressant medication use, and unfavorable events occurring during the first or second pregnancy did not explain the results.

“The mechanism explaining this association is unknown, and more research is needed,” the authors write.

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