Washington D.C., September 24, 2014 - A study published in the October 2014 issue of the Journal of the American Academy of Child and Adolescent Psychiatry found that children who were conceived either less than 1 year or more than 5 years after the birth of their prior sibling were more likely to be diagnosed with autism than children conceived following an interval of 2-5 years.
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."
The article "Increased Risk of Autism Spectrum Disorders at Short and Long Interpregnancy Intervals in Finland" by Keely Cheslack-Postava, PhD, Auli Suominen, MSc, Elina Jokiranta, MA, Venla Lehti, MD, Ian W. McKeague, PhD, Andre Sourander, MD, and Alan S. Brown, MD appears in the Journal of the American Academy of Child and Adolescent Psychiatry, Volume 53, Issue 10 (October 2014), published by Elsevier.
A related editorial, "Sizing Up the Search for Autism Spectrum Disorder (ASD) Risk Markers During Prenatal and Early Postnatal Life," by Dr. Armin Raznahan, is published in the same issue.
This study was funded by the National Institutes of Health (NIEHS R01ES019004 [A.S.B.], NIMH K02 MH065422 [A.S.B.], and NIMH T32-13043 [K.C.P.]), the Turku University Foundation (E.J.), and the Finnish Epilepsy Society (E.J.).
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