Lisa Croen, Ph.D.
Kaiser Foundation Research Institute
NIEHS Grant R01ES016669
A new study, funded in part by NIEHS, found that second-born children conceived less than two years or more than six years after the arrival of their older sibling have an increased risk of autism spectrum disorders. Unlike other studies, the new study ruled out other autism risk factors that might account for the findings.
Previous studies have linked both short and long pregnancy intervals with increased autism risk. To further investigate the link between interpregnancy length and autism, the researchers designed a study that controlled for some potentially confounding factors. Data for the study came from the electronic medical records of about 45,000 children born between 2000 and 2009 in Kaiser Permanente's Northern California hospitals.
Autism was diagnosed in 0.81 percent of second-born children born three to four years after their older sibling. For second-born children with interpregnancy intervals of less than six months, autism prevalence was 2.11 percent; for intervals of six to eight months, 1.74 percent; and for intervals of six years or more, 1.84 percent. The results could not be explained by maternal BMI, change in BMI between pregnancies, parental age, maternal antidepressant medication use, or unfavorable events occurring during the first or second pregnancy.
The researchers say that future studies that incorporate maternal nutritional status, including folate and iron, and other factors such as infertility are necessary to understand the mechanisms involved in the association between autism and interpregnancy intervals.
Citation: Zerbo O, Yoshida C, Gunderson EP, Dorward K, Croen LA. 2015. Interpregnancy interval and risk of autism spectrum disorders. Pediatrics 136(4):651-657.