No form of contraception is 100 percent effective, and a fascinating new study has provided a possible explanation for why that is the case for one of the most widely used forms of birth control. The research has for the first time linked a specificgenetic variant with the efficacy of hormone-based birth controltreatments, suggesting this type of contraception may be less effectivein women found with this particular gene.
The majority ofcurrent birth control drugs work by delivering certain hormones to awoman, preventing her ability to become pregnant. Failure rates forthese contraceptives can vary but generally it is thought that whenproperly and consistently administered, hormonal birth control can be effective up to 99.7 percent of the time.
We don't know exactly why these contraceptives occasionallyfail, and often when they do it is the user who is blamed forincorrectly taking the drug. Maybe a dose was skipped or takenslightly later than it should have been. New research is suggestingfor the first time that it could be a specific genetic variant thatis actually making birth control drugs less effective in some women.
"When a woman says she got pregnant while on birth control theassumption was always that it was somehow her fault," says AaronLazorwitz, from the University of Colorado School of Medicine andlead author on the new study. "But these findings show that weshould listen to our patients and consider if there is something intheir genes that caused this."
Pharmacogenomics is the study of how specific genes influence theeffects of certain drugs. Study into how drug metabolism is affectedby genetics has been around for some time but it is only recentlythat computational power and genomic data has progressed to the pointthat researchers can seriously investigate these connections.
The new research looked at 350 women using a contraceptive implantthat releases etonogestrel, a progestin-based form of hormonal birthcontrol, and focused on a number of genes that govern steroidhormone metabolism and function. One specific gene appeared to play amajor role in enhancing the body's ability to metabolizeetonogestrel.
Called CYP3A7*1C, this gene is primarily active in fetaldevelopment, producing a enzyme called CYP3A7 that alters steroidhormone metabolism. Although it is generally switched off at birth, the research found the gene still remained active in five percent of the womenstudied. Over one quarter of the women with this gene still activewere found to have etonogestrel levels below the recommended limit needed toachieve consistent ovulatory suppression.
"That enzyme breaks down the hormones in birth control and mayput women at a higher risk of pregnancy while using contraceptives,especially lower dose methods," says Lazorwitz.
It is worth noting that this study should not raise concerns forwomen on birth control as these treatments are still incrediblyeffective when used correctly. The research does however highlightthe importance in understanding how a person's unique geneticfingerprint can profoundly influence their ability to metabolizecertain drugs.
It is still early days for this kind of research, andpharmacogenomic tests are not widely available, but Lazorwitz doessuggest this kind of personalized medicine, underpinned by genomicanalysis, will be important in the future, particularly in the realmof women's reproductive health.
"As more genetic data becomes available, clinicians may need toconsider adding genetic predisposition to increased steroid hormonemetabolism in their differential diagnosis for unintended pregnanciesin women reporting perfect adherence to hormonal contraceptivemethods," Lazorwitz concludes.
The new research was published in the journal Obstetrics & Gynecology.
