The Science of Spacing Out Your Kids

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Parents attempt to time their kids’ births for all sorts of reasons—from wanting siblings who are close in age so they’ll be best friends to believing it’s better for one child to soak up Mom and Dad’s attention until the school years before adding another infant to the mix. Now, a new study suggests that in addition to social considerations like these, there may be biological consequences to the spacing of our children.

Research published in the Journal of the American Academy of Child and Adolescent Psychiatry indicates that children conceived either less than one year or more than five years after an older sibling’s birth are more likely to be diagnosed with autism than children conceived within two to five years of an older child’s birth.

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Keely Cheslack-Postava, adjunct associate research scientist at Columbia University, led a group of researchers in analyzing records from the Finnish Prenatal Study of Autism (FIPS-A), which includes a collection of 7371 children born between 1987-2005 in Finland. One third of these children were diagnosed with autism. The risk of autism was 50 percent higher among children conceived within a year of their older siblings, and almost 30 percent higher among those conceived five to 10 years after a sibling.

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“We have seen in several studies now that autism spectrum disorder (ASD) diagnoses have occurred more frequently among children born following closely spaced pregnancies in particular,” Cheslack-Postava tells Yahoo Parenting. She notes that similar patterns of increased risk at shorter and longer inter-pregnancy intervals have been seen for other outcomes, such as low birth weight and preterm birth. “There is a precedent for this type of pattern, and there may be different factors at play for the closely spaced versus distantly spaced births.”

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As for parents thinking about when to add a sibling to their family, Cheslack-Postava stresses that the study doesn’t definitively conclude that keeping conception of later children within 2-5 years of an older child will change the risk of autism. “There could be a factor that changes directly with birth spacing, but there could also be differences in diagnosis or other differences that we could not account for in the analysis,” she says. “My hope is that future studies to understand this pattern will yield new information to help explain the causes of autism.”