PORTLAND, Maine (AP) — A new study finds that the rate of Maine mothers with opioid use disorder at the time of labor and delivery has risen.

Maine Public reports that a U.S. Centers for Disease Control report released this month found Maine had among the highest annual rate of increases among two dozen states studied.

The report says Maine in 1999 saw less than one case per thousand of mothers with opioid use disorder at the time of labor and delivery. By 2014, that number grew to 34 cases per thousand.

The U.S. Centers for Disease Control looked at two dozen states and found that Maine's rate increased by four cases per thousand deliveries each year.