A genetic variant may play a major role in why hormonal contraception fails in some women, according to a new study published in Obstetrics & Gynecology.

To investigate what impact genetic variants have on birth control, researchers from the University of Colorado assessed 350 healthy women who had been using an etonogestrel contraceptive implant for 12 to 36 months. “We collected participant characteristics, measured serum etonogestrel concentrations, and genotyped each participant for 120 single nucleotide variants in 14 genes encoding proteins involved in steroid hormone (ie, estrogens, progestins) metabolism, regulation, or function,” the authors explained.

Using a generalized linear model, they identified 3 genetic variants linked to steady-state etonogestrel concentrations. Of these, the CYP3A7*1C variant was associated with increased etonogestrel metabolism; this gene usually becomes inactive after birth but some women continue to make the enzyme into adulthood. In this patient population, 5.1% of women had the CYP3A7*1C variant, and of these women, 27.8% had etonogestrel concentrations that fell below the threshold for consistent ovulatory suppression (≤90pg/mL).

“As more genetic data becomes available, clinicians may need to consider adding genetic predisposition to increased steroid hormone metabolism in their differential diagnosis for unintended pregnancies in women reporting perfect adherence to hormonal contraceptive methods,” said the study’s lead author Aaron Lazorwitz, MD, assistant professor of Obstetrics and Gynecology at the University of Colorado School of Medicine.

The CYP3A7*1C variant can be identified during genetic screening, suggesting that pharmacogenomics could potentially play a bigger role  in women’s health by providing more personalized approaches.

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This article originally appeared on MPR