Nearly 40% of a reproductive age women enrolled in Medicaid and nearly 30% of those with private insurance filled an opioid prescription between 2008 and 2012, rising concerns that opioid use by women during their peak reproductive years may lead to an increase in birth defects, according to a new report from the Centers for Disease Control and Prevention.

“Many women of reproductive age are taking these medicines and may not know they are pregnant and therefore may be unknowingly exposing their unborn child,” Dr. Tom Frieden, CDC director, said in a statement. “That’s why it’s critical for health care professionals to take a thorough health assessment before prescribing these medicines to women of reproductive age.”

Using claims data, CDC researchers analyzed opioid prescriptions for between 400,000 and 800,000 Medicaid-enrolled women aged 15-44 years, and between 4.4 and 6.6 million privately insured women in the same age range for each year during 2008-2012. The findings were published on Jan. 22 in the Morbidity and Mortality Weekly Report ( 2015;64:37-41 ).

From 2008 to 2012, 39.4% of Medicaid-enrolled women of reproductive age filled an opioid prescription at an outpatient pharmacy, compared with 27.7% among privately-insured women. The year with the highest rate of claims was 2009, with 41.4% of Medicaid-enrolled women and 29.1% of privately insured women filling opioid prescriptions.

The highest subset of opioid prescriptions was in the 30-34 year-old age group for privately insured women (30.9%), and in the 40-44 year-old age group for Medicaid-enrolled women (52.5%).

From 2009 to 2012, there appeared to be a drop in the frequency of opioid use by women of reproductive age, regardless of insurance type, but the researchers urged caution in drawing conclusions about changes over time.

“The apparent decline might indicate improvements in opioid prescribing practices; however, given the potential changes in the composition of the sample used for the privately insured claims data and in the states included in the Medicaid sample each year, this conclusion cannot be drawn from these data,” the researchers wrote.

The most commonly prescribed opioid groups were hydrocodone, codeine, and oxycodone. On average, over the course of the study period, hydrocodone was prescribed 17.5% of the time, followed by codeine (6.9%) and then oxycodone (5.5%) for privately insured women. For women with Medicaid coverage, the rates were higher across the board: 25% for hydrocodone, 9.4% for codeine, and 13.0% for oxycodone.