Higher risk of autism found in children born at short and long interpregnancy intervals

Using data from the Finnish Prenatal Study of Autism (FIPS-A), a group of researchers led by Keely Cheslack-Postava, PhD, of Columbia University, analyzed records from 7371 children born between 1987 and 2005 in Finland. Roughly a third of the children had been diagnosed with autism, while the rest were drawn from other births occurring at similar times and locations. The study used information from several national registries to compare the spacing of pregnancies between the children who had been diagnosed with autism and those who had not.

The study found that the risk of an autism diagnosis among children conceived less than 12 months following a sibling's birth was one and a half times as high as those conceived following an interval of 24-59 months. Children conceived following an interval of 60-120 months were almost 30% more likely to be diagnosed with autism. For intervals of more than 120 months, the risk of autism was over 40% higher.

The analysis accounted for certain factors that might explain the association, such as parents' age, prior number of children, and parental history of psychiatric disorders.

The FIPS-A is a case-control study based in a national birth cohort consisting of all children born in Finland from 1987-2005. It makes use of linked national registries and archived serum samples.

Dr. Cheslack-Postava said of the study, "It was intriguing to see that the risk of ASD diagnosis was higher in both closely and distantly spaced pregnancies. It is important to realize that we can't say from this study that spacing of pregnancies per se is a cause of ASD-this is most likely a proxy of other factors that are more directly related to the chance of the child's developing ASD. In other words, the importance of this finding lies in the clues that it can provide in terms of understanding how the prenatal environment is related to outcomes after birth."

The senior author of the study, Dr. Alan Brown of Columbia University, said, "This study provides further evidence that environmental factors occurring during or near the prenatal period play a role in autism, a serious and disabling condition that afflicts millions of individuals and that is increasing in prevalence. This work also exemplifies the importance of large samples of pregnancies with data acquired during pregnancy and their linkage to comprehensive, national databases of reproductive factors and psychiatric diagnoses."