The number of women giving birth with opioid use disorder quadrupled between 1999 and 2014, a new report from the Centers for Disease Control and Prevention shows.

The increase underscores the severity of the country’s opioid epidemic as a legislative package aimed at helping states curb addiction rates idles in the Senate. Newborns exposed to drugs while in the womb can suffer severe complications, including withdrawal, preterm birth and death.

The CDC study released Thursday found “significant increases” in the number of women with opioid use disorder at the time of delivery in 28 states with available data. The agency analyzed information from a database of inpatient discharges operated by the Agency for Healthcare Research and Quality, finding that the prevalence of pregnant women addicted to opioids increased from 1.5 per 1,000 deliveries in 1999 to 6.5 in 2014.

“These findings illustrate the devastating impact of the opioid epidemic on families across the U.S., including on the very youngest,” CDC Director Robert Redfield said in a statement. “Untreated opioid use disorder during pregnancy can lead to heartbreaking results. Each case represents a mother, a child, and a family in need of continued treatment and support.”

The highest rates existed in Vermont (48.6 cases per 1,000 deliveries) and West Virginia (32.1), according to the report. Washington, D.C. (0.7) and Nebraska (1.2) had the lowest rates.

The CDC reported in March that 63,632 Americans died of drug overdoses in 2016, a 22 percent increase over the previous year. Two-thirds of those deaths were linked to opioids.

The Trump administration has made the opioid epidemic a priority through law enforcement crackdowns, as well as tweaks to prescription drug and treatment regulations under Medicare.

Congress, meanwhile, is looking to pass a package of opioid-related bills this year with several measures aimed at improving care for pregnant women and newborns. The House passed its version in June, but the Senate has yet to finalize its own package.