Obesity and the Pill: Do They Mix?

Peter Kovacs, MD, PhD


May 10, 2013

Contraceptive Failures in Overweight and Obese Combined Hormonal Contraceptive Users

McNicholas C, Zhao Q, Secura G, Allsworth JE, Madden T, Peipert JF
Obstet Gynecol. 2012;121:585-592

Contraception and Obesity

Available forms of contraception provide high but variable degrees of protection against an undesired pregnancy, and most methods are associated with noncontraceptive benefits as well.[1] The most important factor in contraceptive efficacy is adherence.

Hormonal methods, which are highly effective when used properly, are available in the form of tablets, a vaginal ring, a transdermal patch, subdermal implants, and depot injections. Combined (ethinyl estradiol plus progestogen) hormonal methods are available in the form of pills, vaginal rings, and transdermal patches. The contraceptive efficacy of these products was tested mostly in healthy women with normal or close-to-normal body weight.

The number of women who are overweight or obese is on the rise. Obesity affects the metabolism and distribution of several medications and therefore, in the case of hormonal contraceptives, could impair contraceptive efficacy. If the efficacy of contraception is compromised, more undesired pregnancies can be expected, leading to more pregnancy terminations and more obstetric and perinatal complications. It is important to establish the contraceptive efficacy of hormonal methods in obese women.

Study Summary

This report is based on the prospective cohort of women participating in the CHOICE program. Sexually active, reproductive-aged women seeking contraception were provided free long-acting reversible contraceptive methods. McNicholas and colleagues report on 1523 women who elected to use combined hormonal contraceptive pills, vaginal rings, or transdermal patches. Contraceptive failure was defined as a pregnancy that occurred during the use of one these methods.

Participants were grouped according to their body mass index (BMI):

  • < 25 kg/m2: normal;

  • 25-29.9 kg/m2: overweight;

  • 30-39.9 kg/m2: obese; or

  • > 40 kg/m2: morbidly obese.

The pill and ring users had similar baseline characteristics, but the patch users were more likely to be black, had lower incomes and less education, and had experienced more unintended pregnancies in the past. Because contraceptive failure rates were similar for the 3 different delivery systems (5.6% with oral contraceptives, 4.6% with the patch, and 3.4% with the ring), their contraceptive efficacy was combined and analyzed across the BMI categories.

There were 128 unintended pregnancies in the 3 groups. Failure rates did not differ among the BMI categories. Obese women were more likely to be older and black, have less education, and have lower income. Age was negatively associated with unintended pregnancy, whereas increasing parity and history of unintended pregnancies were identified as significant risk factors.