20 October 2010

USA: Hormonal contraceptives for contraception in overweight or obese women

The authors systematically reviewed the evidence on the effectiveness of hormonal contraceptives among overweight and obese women. From Cochrane Database of Systematic Reviews.

The authors note that obesity has reached epidemic proportions around the world. Metabolic changes in obesity and greater body mass may lead to reduced effectiveness of hormonal contraceptives, such as the skin patch, vaginal ring, implants, and injectables. They systematically reviewed the evidence on the effectiveness of hormonal contraceptives among overweight and obese women.

The study’s objective was to examine the effectiveness of hormonal contraceptives in preventing unplanned pregnancies among women who are overweight or obese versus women of lower weight or body mass index (BMI). The authors searched MEDLINE, CENTRAL, POPLINE, EMBASE, ClinicalTrials.gov, and ICTRP. They also contacted investigators to identify other trials.

All study designs were eligible. Any type of hormonal contraceptive could have been examined. The primary outcome was pregnancy. Overweight or obese women must have been identified by an analysis cutoff for weight or BMI (kg/m(2)). Data were abstracted by two authors; life-table rates were included where available. For dichotomous variables, the authors computed an odds ratio with 95% confidence interval. The main comparisons were between overweight or obese women and women of lower weight or BMI.

The authors found 7 reports with data from 11 trials that included 39,531 women. One of three studies using BMI found a higher pregnancy risk for overweight or obese women. In the trial of two combination oral contraceptives, women with BMI >= 25 had greater pregnancy risk compared to those with BMI < 25 (OR 1.91; 95% CI 1.01 to 3.61). Among skin patch users, body weight was associated with pregnancy (reported P < 0.001) but BMI was not. Studies of a vaginal ring (never marketed) and a six-rod implant showed higher pregnancy rates for women weighing >= 70 kg versus those weighing < 70 kg (reported P values: 0.0013 and < 0.05, respectively). However, two implant studies showed no trend by body weight, and trials of an injectable had no pregnancies.

The authors conclude that body weight addresses overall body size, while BMI generally reflects the amount of fat. Only one of three studies using BMI found a higher pregnancy risk for overweight women. The efficacy of implants and injectable contraceptives may be unaffected by body mass. The field could use trials of contraceptive methods with groups stratified by BMI. The current evidence on effectiveness by BMI is limited. However, the contraceptive methods examined here are still among the most effective when the recommended regimen is followed.

Behavioral and Biomedical Research, FHI, P.O. Box 13950, Research Triangle Park, North Carolina, USA, 27709.

Hormonal contraceptives for contraception in overweight or obese women. Lopez LM, Grimes DA, Chen-Mok M, Westhoff C, Edelman A, Helmerhorst FM. Cochrane Database of Systematic Reviews. 2010 Jul 7;(7):CD008452.