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Study: Autism More Likely In Closer-Spaced Pregnancies

January 10, 2011

The sooner a second child is conceived following the birth of his or her older sibling, the higher the risk that that boy or girl will develop autism, claims a new study in Monday’s edition of the journal Pediatrics.

The study, which evaluated over 660,000 children in the state of California, discovered that having a second child less than two years after the first makes that infant “considerably more likely to have an autism diagnosis compared to those born after at least three years,” AP Medical Writer Carla K. Johnson said, adding that the effect “was found for parents of all ages, decreasing the chance that it was older parents and not the birth spacing behind the higher risk.”

Furthermore, according to Genevra Pittman of Reuters Health, “Of all second siblings whose mothers became pregnant with them less than a year after giving birth to the older sibling, about 7.5 in every 1,000 were diagnosed with autism. When mothers became pregnant three years or more after giving birth, about 2.5 out of every 1,000 younger siblings were diagnosed with autism.”

The authors told Reuters Health that they aren’t sure whether or not the younger siblings are actually more likely to be autistic or if parents are just more aware of possible signs of the disorder because of their recent experience with another growing child. One possible explanation, according to what lead author Dr. Keely Cheslack-Postava of Columbia University told Pittman, is that there’s a biological or nutritional factor, perhaps in the mother, that makes the second child more at risk for autism.

Peter Bearman, also of Columbia University and credited by Johnson as a senior author on the study, called the results “pretty shocking”¦ No matter what we did, whether we were looking at autism severity, looking at age, or looking at all the various dimensions we could think of, we couldn’t get rid of this finding.”

Bearman, Cheslack-Postava, and their colleagues looked at births in California from 1992 through 2002, and according to the AP, their study used information from the state’s Department of Developmental Services to study second-born children whose older siblings had not been diagnosed with autism or a similar spectrum disorder. In all cases, less than one percent of the kids were autistic.

The research was sponsored by the Robert Wood Johnson Foundation, an agency that says it is dedicated to improving healthcare in the U.S., and the National Institutes of Health (NIH).

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