Washington, April 30 (IANS): The number of infants born in the US with drug withdrawal symptoms has nearly doubled in a four-year period, a new study says.

Also termed the neonatal abstinence syndrome (NAS), the symptoms have been linked to both illicit drug use as well as use of prescription opioids - narcotic pain relievers - by pregnant women.

Infants born with NAS are more likely to have respiratory complications, feeding difficulty, seizures and low birth-weight.

"The rise in neonatal abstinence syndrome mirrors the rise we have seen in opioid pain reliever use across the nation," said study lead author Stephen Patrick, assistant professor of Paediatrics at Vanderbilt University in Nashville, Tennessee.

The study found that from 2009 to 2012, the incidence of neonatal abstinence syndrome rose in the US from 3.4 births per 1,000 to 5.8 births per 1,000.

Tennessee, Kentucky, Mississippi and Alabama had the highest rates of the syndrome, occurring in 16.2 hospital births per 1,000.

Previous research studies have shown opioid pain reliever use skyrocketing in the past decade. In 2012 alone, physicians in the US doled out an estimated 259 million opioid prescriptions, enough for every American adult to have one bottle.

"Pregnant women are commonly being prescribed opioid pain relievers, increasing the likelihood their infants are born with NAS," Patrick noted.

The study was published in the Journal of Perinatology.