Dr. Stephen W. Patrick, a fellow in the University of Michigan's Division of Neonatal-Perinatal Medicine, the estimated number of newborns with drug withdrawal syndrome was 13,539 -- or about one baby born each hour -- by 2009.

"Recently, the Centers for Disease Control and Prevention released a report which found that over the last decade sales for opiate pain relievers like OxyContin and Vicodin have quadrupled," Patrick said in a statement. "Although our study was not able to distinguish the exact opiate used during pregnancy, we do know that the overall use of this class of drugs grew by five-fold over the last decade and this appears to correspond with much higher rates of withdrawal in their infants."

Patrick said multiple factors are likely responsible for the spike in use of opiate pain relievers, from their potential overuse for chronic pain to illegal sales of these drugs on the street.

The study, published in the Journal of the American Medical Association, showed the number of mothers using opiate drugs increased five times over the last decade.

"You can often stand in the hallway and know which babies are experiencing withdrawal. They are irritable, their cries are different and they appear uncomfortable," Patrick commented. (UPI)