Use of safe and effective contraception is essential for preventing unintended pregnancy. Despite the need for contraception, a national survey in the United States noted that sexually active obese women of reproductive age were significantly less likely to use contraception than women of normal weight . It was unclear whether the disparity was due to patient, provider, and/or systems issues.
When counseling obese women about contraception, it is important to consider how obesity may affect the safety and efficacy of various contraceptive methods. Because contraceptive clinical trials excluded overweight or obese women until recently, evidence regarding contraceptive effectiveness and safety for this population is limited [2,3]. This topic will address the effects of obesity on contraceptive efficacy, as well as the effects of contraceptives on weight gain. Fertility and pregnancy issues in obese women are reviewed separately. (See "The impact of obesity on female fertility and pregnancy".)
Guidelines from the World Health Organization (WHO) (table 1) and United States Centers for Disease Control (CDC) Medical Eligibility Criteria for Contraceptive Use (table 2) are helpful for advising obese women about the safety of contraceptive methods [4,5].
For obese women ≥18 years of age without coexistent medical issues, the CDC Medical Eligibility Criteria for Contraceptive Use categorizes progestin-only contraceptives and copper-releasing intrauterine device (IUD) as class 1, which means that there are no restrictions in the use of these methods for obese women . Estrogen-containing contraception (pill, patch, ring) are categorized as class 2, which means that the advantages of using the method generally outweigh the theoretical or proven risks. The class 2 rating is based on data that obesity is an independent risk factor for venous thrombosis (VTE) and case-control studies suggest that this risk is additive in users of estrogen-containing contraceptives [6-8]. Of note, the Faculty of Family Planning and Reproductive Health Care in the United Kingdom assigned estrogen-containing contraceptives for women with body mass index (BMI) 35 to 39 and ≥40 kg/m2 a class 3 and a class 4 rating, respectively . Class 3 refers to a condition where the theoretical or proven risks usually outweigh the advantages of using the method and class 4 refers to a condition which represents an unacceptable health risk if the contraceptive method is used. However, there is no consensus that this distinction is needed , and no safety data are available for women with BMI ≥40 kg/m2 .
The presence of risk factors for VTE should be taken into account when counseling obese women about the risks of estrogen-progestin contraceptives. We offer estrogen-progestin contraceptives to obese women older than 35 years of age as long as they do not have other medical contraindications to use of these drugs. In epidemiologic studies, increasing age is consistently associated with an increased risk of VTE; however, the prevalence of comorbidities associated with increased VTE risk is also increased with increasing age. This makes the impact of age on VTE risk difficult to determine, particularly in reproductive aged women in whom the absolute incidence of VTE is low (see "Overview of the causes of venous thrombosis"). The 2010 CDC Medical Eligibility Criteria for Contraceptive Use category 2 rating (a condition for which the advantages of using the method generally outweigh the theoretical or proven risks) for estrogen-containing contraceptives applies to women ≥30 kg/m2 regardless of age .