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Autism Linked to Low Birth Weight

Study Shows Increased Risk of Autism in Low Birth Weight or Preterm Babies
By
WebMD Health News
Reviewed by Louise Chang, MD

Low Birth Weight Autism

June 2, 2008 -- Low birth weight and preterm birth increase the risk of autism in infants by about twofold, but more so for girls than for boys, according to a new study.

The research bolsters the suspected link between autism, low birth weight, and prematurity.

"We saw this difference in risk between boys and girls," says Diana Schendel, PhD, lead health scientist at the National Center on Birth Defects and Developmental Disabilities at the CDC in Atlanta. The gender finding was unexpected, she says, especially since autism is much more common in boys. Schendel is a researcher of the study, published in Pediatrics.

When the 565 boys and girls with autism were looked at separately, the boys had less than a twofold increased risk of autism if they were born at low birth weight, but the low-birth-weight girls had a threefold or higher risk, found Schendel and her CDC colleague Tanya Karapurkar Bhasin, MPH.

They also found that low birth weight (less than 5.5 pounds) and early preterm birth (less than 33 weeks' gestation) affected groups of children differently, depending on whether they had autism alone or autism and other developmental disabilities.

"There may be a lot of variation in the endpoint we call autism," Schendel tells WebMD. The study result, she says, "really is highlighting that we aren't looking for one cause of autism." The study builds on previous research, some of which has also found a link between low birth weight and autism.

"What is new in this study is the in-depth look at the gender effect," she says. The analyses of different groups classified by number and type of disability also add new information.

Study Details: Autism and Low Birth Weight

The researchers examined the records of 565 children with autism, born in Atlanta from 1986 to 1993, matching them to a control group of children. They looked at whether the children were born early, small, or both, and whether they had autism and other developmental problems.

The children with autism were further divided into three groups: those who had autism but no other developmental disabilities, those with autism who also had an intellectual disability, and those with autism and more than one other developmental disability.

About one in 150 children in the U.S. now have autism or related disorders that fall on what is known as the autism spectrum, according to the CDC.

Overall, the researchers found that a birth weight below 5.5 pounds was associated with a 2.3-fold increased risk for autism. Although preterm birth earlier than 33 weeks was not statistically linked to autism for boys, there was a significant fivefold increased risk seen for girls with autism.

The researchers then looked at the subgroups, divided by type and number of disability, and found variations. For instance, the increase in risk for autism in low-birth-weight girls with mental retardation was fourfold, while the increased risk found in low-birth-weight boys just for developing autism was not statistically significant.

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