A baby is born every hour with signs of opiate drug withdrawal, according to a new U.S. study -- and the number of newborns in withdrawal has tripled over the past decade.

Those babies are born earlier than average and with a higher risk of breathing problems and seizures, and they require careful monitoring and treatment to wean them off the drugs before they can go home.

Researchers also found that the number of new moms who tested positive for use of opiates -- which include powerful painkillers such as oxycontin -- increased five-fold between 2000 and 2009. In the most recent study year, between five and six out of every 1,000 women had the drugs in their system.

"This study is part of a bigger call to the fact that opiates are becoming a big problem in this country," said Dr. Stephen Patrick from the University of Michigan in Ann Arbor, who worked on the study. It's unclear whether there are long-term health effects for babies, but some research shows a higher risk of developmental problems, according to Patrick.

According to the Centers for Disease Control and Prevention, 14,800 people died of a prescription drug overdose in 2008 -- triple the estimate from 20 years earlier.

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