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Gestational age affects autism severity, study finds


For children with autism, being born several weeks early or several weeks late tends to increase the severity of their symptoms, according to new research.

Additionally, autistic children who were born either preterm or post-term are more likely to injure themselves compared with autistic children born on time, revealed the study by researchers with Michigan State University.

Although the study did not uncover reasons for the increase in autistic symptoms, the association may be tied to some of the underlying causes for preterm (before 37 weeks) or post-term (after 42 weeks) births.

Lead researcher Tammy Movsas, MD, a postdoctoral epidemiology fellow in MSU’s College of Human Medicine, said the study reveals a variety in manifestations of autism spectrum disorder, and shows the length of the mother’s pregnancy is one factor affecting severity.

Although previous research has linked premature births to higher rates of autism, the researchers said this study is among the first to look at the severity of the disease among autistic children born early, on time and late.

“We think about autism being caused by a combination of genetic and environmental factors,” Movsas said, according to an MSU news release. “With preterm and post-term babies, there is something underlying that is altering the genetic expression of autism.

“The outside environment in which a preterm baby continues to mature is very different than the environment that the baby would have experienced in utero. This change in environment may be part of the reason why there is a difference in autistic severity in this set of infants.”

Movsas added that for post-term babies, the longer exposure to hormones while a baby is in utero, the higher chance of placental malfunction and the increased rate of C-section and instrument-assisted births may play a role.

The study also found that babies born outside of normal gestational age (40 weeks) — and especially very preterm babies — showed an increase in stereotypical autistic mannerisms.

“Normal gestation age of birth seems to mitigate the severity of autism spectrum disorder symptoms, and the types of autistic traits tend to be different depending on age at birth,” Movsas said.

The study analyzed a 2006-10 online database compiled by the Kennedy Krieger Institute at Johns Hopkins University of nearly 4,200 mothers with autistic children ages 4 to 21. It divided the data on births into four categories: very preterm (born before 34 weeks), preterm (34 to 37 weeks), standard (37 to 42 weeks) and post-term (born after 42 weeks).

The mothers filled out a pair of questionnaires regarding the symptoms of their autistic children, and the results revealed very preterm, preterm and post-term autistic children had significantly higher screening scores for autism spectrum disorder than autistic children born full term.

The study appears on the website of the Journal of Autism and Development Disorders. To access the study via subscription or purchase, visit


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