Neonatal abstinence syndrome (NAS), a drug withdrawal syndrome in infants following birth, has historically been associated with illicit drug use among pregnant women.

However, researchers at Vanderbilt University Medical Center found that pregnant women are commonly being prescribed narcotic pain relievers such as hydrocodone -- which contains opioids -- which results in an increased likelihood of NAS.

They also found that opioid type and duration of exposure combined with tobacco use or selective serotonin reuptake inhibitor use (for treating depression and anxiety) augmented risks for NAS.

"We found that babies exposed to opioids pain relievers were more likely to be born preterm, have complicated births, low birth weight and have complications such as meconium aspiration syndrome (a sign of infant distress at birth) and respiratory distress," Stephen Patrick, lead author of the study, said in a statement.

For the study, researchers looked at three years of data from TennCare, Tennessee's Medicaid program, and assessed records for 112,029 pregnant mothers. An estimated 28 percent of the women, or 31,354, were prescribed and filled at least one opioid pain reliever. Of the babies with NAS, 65 percent had mothers that legally filled prescriptions for opioid pain relievers.

"Not all babies exposed to opioids have drug withdrawal after birth for reasons that aren't entirely clear. Our study found that several things increased an infant's risk, including the duration of opioid use, the type of prescription opioid, how many cigarettes a woman smoked and if they used a common antidepressant medicine called selective serotonin reuptake inhibitors."

The study shows that compared to women with no opioid exposure, the pregnant women who took opioid pain relievers were more likely to be white, have anxiety or depression, suffer from headache or migraine and have musculoskeletal disease. A majority of the women prescribed opioids, 96 percent, were prescribed short-acting medications, while 2 percent received maintenance doses and less than 1 percent received long-acting opioids.

"Historically, drug withdrawal for newborns has been described among illicit drug use such as heroin or women treated for previous opioid abuse, but this is really one of the first studies to look at legal prescriptions for pregnant women. And it draws attention to what is going on in our nation," Patrick said.

Nationwide, the amount of prescriptions for opioid drug use has quadrupled. In 2012, an estimated 259 million prescriptions were written for opioid pain relievers in the United States. That's enough for one prescription for every adult in the United States, according to Patrick.

The findings are detailed in the journal Pediatrics.