Obesity Linked to the Birth Control Pill Failure

Jul 25, 2009
Obese women are more likely to get pregnant while using birth control pills, a new study suggests.

Birth control pills work in a different way for women with extra weight if compared to normal-weight women.

Dr Alison B. Edelman, the author of the study at Oregon Health and Science University in Portland says that obesity may change drug metabolism in the body, which decreases its effectiveness.The study included 20 volunteers, aged between 18 and 35, who were not on the pill. They were asked to take the combined birth control pills, containing levonorgestrel and ethinyl estradiol for two cycles. Measurements of BMI (Body mass Index) were taken from all the women, who were then divided into two groups. The first group of participants had BMIs of more than 30, while the other group had BMIs of less than 20.

The findings showed that for the obese women the level of levonorgestrel in the blood reached its steady state level after 10 days of taking the pill, while for normal weight women it took only 5 days.

The fact that it took longer for obese women to reach the steady state level of levonorgestrel indicates that this may increase the possibility of ovulation and thus pregnancy. It was also found that for one woman it took as much as 20 days for the pill to work, which may actually fail to suppress the ovulation.

The scientists say that further studies are needed, because the study did not involved overweight women and the results did not analyzed whether the women had ovulation or not.

The study wasp published in the recent issue of the journal Contraception.