New research suggests the spacing of pregnancies may play a factor in the development of autism spectrum disorder (ASD).
Investigators discovered children who were conceived either less than one year or more than five years after the birth of their prior sibling were more likely to be diagnosed with autism than children conceived following an interval of two to five years.
The research is published in the Journal of the American Academy of Child and Adolescent Psychiatry.
Keely Cheslack-Postava, Ph.D., of Columbia University and a group of researchers analyzed records from the Finnish Prenatal Study of Autism (FIPS-A), a collection of 7371 children born between 1987 and 2005 in Finland.
Their review found that 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 percent more likely to be diagnosed with autism.
For intervals of more than 120 months, the risk of autism was over 40 percent higher.
Investigators say the analysis adjusted 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.
“It was intriguing to see that the risk of ASD diagnosis was higher in both closely and distantly spaced pregnancies,” Cheslack-Postava said.
“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, Alan Brown, M.D., M.P.H., 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.”