NEW YORK (AP) — Health officials are looking into a possible link between prescription opioids and a horrific birth defect.

When a baby is born with its intestines hanging outside the stomach, due to a hole in the abdominal wall, it's called gastroschisis. Most are repaired through surgery.

Roughly 1,800 such cases are seen in the U.S. each year, but the number has been rising and officials don't know why.

The condition seems to occur more often when the mom is a teenager or was smoking or drinking alcohol early in pregnancy, researchers have noted.

But a study released Thursday noted cases were 60 percent more common in counties that had the highest overall opioid prescription rates. The Centers for Disease Control and Prevention study focused on 20 states.

The study did not see if each mother had been taking opioids, and it does not say opioids caused the birth defects. But it echoes earlier research that found a higher risk of birth defects when moms took opioid painkillers like oxycodone just before or early in pregnancy.

Also Thursday, the CDC's director and two other agency officials wrote a commentary in the journal Pediatrics urging more study of the possible connection between opioids and birth defects.

"The report sounds an early alarm for the need to increase our public health surveillance on the full range of fetal, infant, and childhood outcomes potentially related to these exposures," wrote CDC Director Dr. Robert Redfield and his two co-authors.

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