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Shorter time between pregnancies linked with increased autism risk
Cheslack-Postava K. Pediatrics. 2011;doi:10.1542/peds.2010-2371.
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The closer two siblings are born together, the higher the risk for autism in the second child, according to a study.
Keely Cheslack-Postava, PhD, of Columbia University in New York, and colleagues reported the results of 662,730 second-born children in California. The researchers said the children born less than 2 years after their siblings were more likely to have autism compared with those born after 3 years, even after they adjusted for a variety of sociodemographic factors.
This effect was noted across age groups, which the researchers said decreased the chances that the autism was related to older age at conception; however, women are more frequently delaying childbirth, which is leading to an increase in closely spaced births. The researchers cited national data that showed an increase from 11% to 18% between 1995 and 2002 in the number of births that are spaced less than 2 years apart.
The researchers looked at birth records from 1992 to 2002. The information on autism diagnoses came from the California Department of Developmental Services. Of the 662,730 second-born children, 3,137 had an autism diagnosis.
The researchers said interpregnancy intervals (IPIs) of less than 12, 12 to 23 and 24 to 35 months “were associated with odds ratios (95% confidence intervals) for autism of 3.39 (3.00-3.82), 1.86 (1.65-2.10), and 1.26 (1.10-1.45) relative to IPIs of ≥36 months.”
The mother’s physiology could play a role in the autism spike because pregnancy depletes a mother’s nutrients, particularly folate, and other research has tied this lack of nutrients to other developmental issues such as low birth weights and prematurity, the researchers said. They added that parents may also be more likely to pick up on the developmental differences between siblings if they are closer in age, and thus be more likely to seek help.
“In some, although not all studies, parents of children with autism have reported first having concerns about their child’s development earlier when there was an older sibling,” the researchers said. “If this explains some of the association observed here, it may indicate a need for increased attention to developmental surveillance, especially where parents are less familiar with patterns of typical development.”
Disclosure: The study was supported by the Robert Wood Johnson Foundation Health and Society Scholars Program and the NIH. The researchers reported no relevant disclosures.
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