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Autism Spectrum Disorders Health Center

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Autism Linked to Low Birth Weight

Study Shows Increased Risk of Autism in Low Birth Weight or Preterm Babies

Study Details: Autism and Low Birth Weight continued...

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.

Schendel can't explain why the low-birth-weight girls were found to have a greater risk than the low-birth-weight boys. Both low birth weight and preterm birth are markers, she says, that something may have gone wrong during the pregnancy. The poor fetal growth resulting in low birth weight may be associated with developmental problems. Or, on the other hand, low birth weight may be a marker of a fetus that's already adversely affected neurologically, she says.

"We don't know if it's the low birth weight ... causing brain damage, or whether the brain damage has occurred and low birth weight is the consequence," she tells WebMD.

Second Opinion: Low Birth Weight and Autism

The study is scientifically solid, says Susan Hyman, MD, an autism researcher and an associate professor of pediatrics at the University of Rochester Medical Center, University of Rochester School of Medicine, N.Y. She chairs the autism expert panel of the American Academy of Pediatrics.

Though previous research has yielded conflicting findings about the low birth weight-autism link, "I think this study comes close to laying the debate to rest," Hyman says.

"Pediatricians are very aware to monitor babies [born prematurely or at low birth weight] that require neonatal intensive care unit care for any sort of developmental difficulties," she says. But autism has not been targeted specifically; this study may make them more aware, she says.

Under the academy's developmental surveillance guidelines, Hyman says, children born early and small should be monitored for developmental disabilities. And the academy recommends routine screening for autism at 18, 24, and 30 months and also when there are parental concerns, she says.

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