Study Indicates Increased Rate of Autism with Closely Spaced Pregnancies

A study published in the February issue of Pediatrics, suggests that babies born close together may triple the risk of autism in the second child.  The researchers hypothesize that the first pregnancy may deplete critical nutrients such as folate and iron, and the mother may also be more stressed during the second pregnancy. 

The highest risk was seen in babies conceived within a year of their older sibling. Babies conceived within 12 to 23 months and 24 to 35 months of their older sibling were also at a heightened risk of autism, although the risk was not as pronounced.

Researchers looked at birth records for about 660,000 second-born children born in California between 1992 and 2002. Autism diagnoses were confirmed using records from the California Department of Developmental Services.

Second-born children conceived within a year of the birth of the first-born children were more than three times as likely to have autism than children conceived more than three years apart.

In addition, babies conceived within 12 to 23 months had nearly twice the risk of having autism, while babies conceived between 24 and 35 months were 26 percent more likely to have autism, the investigators found.

-February Pediatrics Journal

The findings are especially important because of the trend in women having babies closer together. Between 1995 and 2002, the proportion of births occurring within 24 months of a previous birth increased from 11 percent to 18 percent.  Many times women who are racing the biological clock tend to have babies closer together.

Overall the incidence of autism has been rising.  According to Autism Speaks, a leading science and advocacy organization, it is estimated that 1 in 110 children in US are diagnosed with autism. Government statistics suggest the prevalence rate of autism is increasing 10 to 17 percent annually.

Closely spaced pregnancies could be one, but definitely not the only factor driving the increase in autism, per Shih. 

SOURCES: Keely Cheslack-Postava, Ph.D., postdoctoral research scholar, Columbia University, New York City; Andy Shih, Ph.D., vice president, scientific affairs, Autism Speaks, New York City; February 2011, Pediatrics