Study: Failed Birth Control May Be Linked to Gene

By Dorothy L. Tengler via Multibriefs

Of women ages 15 to 44 years, nearly 16% use the pill for birth control, 8% use long-acting reversible contraception such as an intrauterine device or contraceptive implant, and 14% use female sterilization. The pill is the most commonly used form of birth control in the U.S., and when taken as directed is 99.7% effective.

Different birth control methods may be highly effective for preventing pregnancies, but birth control failure is more common than many realize. Almost half of the over 6 million pregnancies in the U.S. are accidents, often because women either forget to or don’t use the method as directed.

However, the rate of unintended pregnancy declined 18% between 2008 and 2011, from 54 per 1000 women aged 15-44 to 45 per 1000, suggesting that more effective contraceptive use over time (i.e., more consistent and correct use, more users switching to more effective methods or both) may have contributed to recent declines in unintended pregnancy.

But about 5% of the time, women using reliable birth control find themselves unexpectedly pregnant, and until now, the main reason was thought to be that the birth control method wasn’t being used correctly.

A new study suggests that women who get pregnant while using birth control may carry a gene that breaks down the hormones common in contraceptives.

Aaron Lazorwitz, MD, assistant professor of Obstetrics and Gynecology at the University of Colorado School of Medicine, and his colleagues, suspecting that there may be other reasons for birth control failure, looked at 350 healthy women (median age, 22.5 years) who had a contraceptive implant in place for between 12 and 36 months. They found that 5% of women tested had a gene called CYP3A7*1C that is usually active in fetuses and then switched off before birth.

Surprisingly, some women with this gene continue to make the CYP3A7 enzyme into adulthood. This enzyme breaks down the hormones in birth control and may put women at a higher risk of pregnancy while using contraceptives, especially lower dose methods. Genetic screening can identify this variant.

The implications of this study suggest that pharmacogenomics, a new field that analyzes how genes affect our response to drugs, may help alter the field of women's health, particularly regarding the social, financial, and emotional consequences of contraceptive failure and unwanted pregnancies.

According to Lazorwitz, the study may encourage the development of specialized medical tools that can help tailor treatment to individual patients.

Dorothy L. Tengler, MA, is a freelance medical writer/communication specialist with nearly 20 years of experience in the pharmaceutical and medical communication industries. She has developed educational and medical marketing materials, including monographs, slide kits, health articles, primary and review manuscripts, and pharmaceutical sales training materials.