Researchers at the Mailman School of Public Health, the Department of Psychiatry at Columbia University, and the New York State Psychiatric Institute found that 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. Findings are online in the Journal of the American Academy of Child and Adolescent Psychiatry.
The researchers analyzed records from 7371 children born between 1987 and 2005 in Finland using data from the Finnish Prenatal Study of Autism (FIPS-A), a case-control study based in a national birth cohort consisting of all children born in Finland from 1987-2005 that makes use of linked national registries and archived serum samples. The results showed 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% 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.
“It was intriguing to see that the risk of autism spectrum disorder diagnosis (ASD) was higher in both closely and distantly spaced pregnancies,” said Dr. Cheslack-Postava, in the department of psychiatry and who was a postdoctoral fellow in epidemiology at the Mailman School of Public Health when the research was conducted. “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.”
“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,” said senior author Dr. Alan Brown, Mailman School professor of epidemiology and professor of psychiatry at Columbia University Medical Center and the New York State Psychiatric Institute. “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.”
The study was funded by the National Institutes of Health R01ES019004, National Institute of Mental Health K02 MH065422 and T32-13043, the Turku University Foundation, and the Finnish Epilepsy Society.