Scientists Think a Gene Causes Birth Control to Fail in Some Women

"We have just always assumed a woman had done something wrong."

Pregnancy

Today, there are a variety of contraceptives available that greatly lower the odds of becoming pregnant, but there’s no guarantee attached to any one method.

While ineffectiveness is often blamed on women not taking their birth control properly, new research suggests some women carry a gene that breaks down the hormones commonly found in contraceptives, meaning that they can still become pregnant even if they use hormonal birth control. A study on the gene was published Tuesday in Obstetrics & Gynecology.

Dr. Aaron Lazorwitz, an associate professor of Obstetrics and Gynecology at the University of Colorado School of Medicine, tells Inverse that the assumption that a woman did something wrong with her birth control and that’s why she’s pregnant has been a pervasive problem in the health care industry.

Lazorwitz says he and his colleagues (there were at least four women on the research team) suspected something besides human error could be a factor, and they looked into the field of pharmogenomics, which is the study of the relationship between genetic variations and interindividual variability in drug response.

It puzzled Lazorwitz why no one had examined how pharmogenomics linked to women’s health before. While women are essentially given the same hormones to prevent pregnancy, doctors haven’t considered whether hormones would work the same for all patients.

birth control pill
The team suspects what they found here could be applied to the pill.

“We have all seen women come in saying that they got pregnant when they were adamant that they were taking the pill every day or using a different birth control method perfectly,” Lazorwitz says. “It seems that for the longest time we have just always assumed a woman had done something wrong when using her birth control, instead of considering whether there were other factors affecting how birth control works in individual women.”

Is It the Gene CYP3A7*1C?

One of these factors, this study argues, could very well be a gene called CYP3A7*1C. This gene is usually active in fetuses and switched off before birth — it’s not yet known what role it serves in the fetal stage of life or why it’s often not found in adults.

Lazorwitz and his colleagues found that some women do retain this genetic variant. They examined 350 healthy women with a median age of 22.5 years old who have had a contraceptive implant in place for between 12 and 36 months. Five percent of these women tested positive for CYP3A7*1C.

Further investigation revealed that the gene caused an expression of enzymes that can break down the steroid hormones found in birth control. While none of the women in the study with this gene became pregnant, they did test positive for lower hormone levels compared to the other women with the implant.

“We used implant users because it is the most effective hormonal contraceptive method we have, and it is the easiest method to look at how genetic differences affect the amount of hormones in each woman’s system that is released from the implant,” Lazorwitz explains. “The implant releases a steady, consistent amount of hormone over time and there should be almost no difference in the amount each woman is getting from the implant, but the measured hormone levels are widely different between women.”

IUD, birth control
IUDs are 99 percent effective.

According to Planned Parenthood, birth control implants and IUDs are 99 percent effective, while the pill sits at 91 percent.

The team thinks this research could be applicable to other hormonal contraceptive methods, like the pill. However, Lazorwitz cautiously notes that despite that confidence, it’s still a theoretical connection that needs to be studied further and the eventual plan is to conduct this study again with women who use the pill.

Until then, Lazorwitz hopes this information will influence doctors to consider factors outside of a woman’s control when she tells them she has become pregnant while on birth control.

“I also hope that this research will inspire others to start asking more questions about genetics and women’s health, so that we can figure out how important some of these variants are, like CYP3A7*1C, and one day develop tools to help us provide individualized counseling to patients about the best hormonal medications for them,” Lazorwitz says. “We’re definitely not there yet, but this study is hopefully the first stepping stone in that process.”

Abstract:

Only BMI and duration of implant use remained significantly associated with steady-state etonogestrel concentrations. Of the three novel genetic associations found, one variant associated with increased etonogestrel metabolism (CYP3A71C) causes adult expression of fetal CYP3A7 proteins and can consequently alter steroid hormone metabolism. Women with this variant may potentially have increased metabolism of all steroid hormones, as 27.8% (5/18) of CYP3A71C carriers had serum etonogestrel concentrations that fell below the threshold for consistent ovulatory suppression (less than 90 pg/mL). More pharmacogenomic investigations are needed to advance our understanding of how genetic variation can influence the effectiveness and safety of hormonal contraception, and lay the groundwork for personalized medicine approaches in women’s health.