MONDAY, Jan. 10 (HealthDay News) -- Second-born children born after an interpregnancy interval (IPI) of less than one year appear to be at a substantially higher risk of autism than those with IPIs of at least 36 months, according to a study published online Jan. 10 in Pediatrics.
Using birth records, Keely Cheslack-Postava, Ph.D., M.S.P.H., of Columbia University in New York City, and colleagues identified pairs of first- and second-born singleton full siblings from all California births that occurred from 1992 to 2002; autism diagnoses were noted using linked records of the California Department of Developmental Services. The researchers calculated IPI as the time interval between birth dates minus the second sibling's gestational age.
Among 662,730 second-born children, the investigators found an inverse association between IPI and odds of autism. IPIs of less than 12 months were associated with odds ratio for autism of 3.39 compared to IPIs of at least 36 months. In addition, IPIs of 12 to 23 months and 24 to 35 months were associated with odds ratios of 1.86 and 1.26, respectively, compared with IPIs of at least 36 months. The investigators found that second-born children were at a higher risk of autism relative to their first-born siblings only in pairs with short IPIs.
"These results suggest that children born after shorter intervals between pregnancies are at increased risk of developing autism; the highest risk was associated with pregnancies spaced less than one year apart," the authors write.
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