Hormonal contraceptives for contraception in overweight or obese women

Excess body weight has become a problem around the world. Being overweight or obese may affect how well hormonal birth control works to prevent pregnancy.  Hormonal birth control includes birth control pills, the skin patch, the vaginal ring, implants, and injectables. We looked at studies of hormonal birth control for women who were overweight or obese compared to women of normal weight or body mass index (BMI). The formula for BMI is weight (kg) / height (m)2.We did computer searches for hormonal birth control among women who were overweight or obese. We also wrote to researchers to find other studies we might have missed in our search. All types of studies were considered.We found 7 reports with data from 11 trials and 39,531 women. One of three studies using BMI found more pregnancies among overweight or obese women. That trial looked at two birth control pills. Studies of an early vaginal ring (never marketed) and of a six-rod implant showed the women weighing 70 kg or more had more pregnancies than those weighing less than 70 kg. Among skin patch users, more pregnancies were found among women weighing 80 kg or more. However, the researchers reported that BMI was not related to pregnancy. Two implant studies showed the body weight groups to be similar for pregnancy. Trials of an injectable method had no pregnancies.Body weight shows overall body size, while BMI reflects the amount of fat. Only one of three studies using BMI found more pregnancies among overweight or obese women. Three of five reports using body weight showed a difference. Body size might not affect how well implants and injectable methods work to prevent pregnancy. Counseling women about how well birth control methods work is hard with little information on any one method. The field could use randomized trials of birth control methods with the groups divided by BMI. However, the birth control methods studied here are among the most effective when the directions are followed.