Pregnant opioid addicts have increased fourfold in the U.S. over the past 15 years, a report by the US Centers for Disease Control and Prevention revealed.
The first major national study of its kind, the report revealed "significant increases in the 28 states with available data" from 1999 to 2014, AFP reported.
"These findings illustrate the devastating impact of the opioid epidemic on families across the US, including on the very youngest," said CDC Director Robert Redfield.
"Untreated opioid use disorder during pregnancy can lead to heartbreaking results."
Women who abuse opioids while pregnant risk maternal death, preterm birth, and stillbirth. Their babies, if born alive, are often addicted to the potent drugs themselves and must go through a period of painful withdrawal known as neonatal abstinence syndrome.
"Opioid use by pregnant women represents a significant public health concern," said the CDC report.
Nationwide, the rate of women with "opioid use disorder" arriving at hospitals to deliver their babies "increased from 1.5 per 1,000 delivery hospitalizations in 1999 to 6.5 in 2014," it said.
The report did not specify what kinds of opioids the women were using.
The United States is grappling with a surging epidemic of opioid abuse -- including painkillers like OxyContin and street drugs like heroin -- which took more than 42,000 lives in 2016.
The CDC said excessive prescribing practices by doctors could be a factor in opioid abuse, and called for increased efforts to prevent women from becoming addicted and help them get treatment.