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".)
CHOOSING A CONTRACEPTIVE METHOD
Many factors need to be considered in choosing a contraceptive method (see "Overview of contraception", section on 'Choosing a method of contraception'). For obese women who want to maximize safety and efficacy, we suggest a copper- or levonorgestrel-releasing intrauterine device (IUD). Intrauterine contraception has a very low rate of failure (compared with barrier methods), is not associated with weight gain (compared with depot medroxyprogesterone acetate [DMPA]), and does not expose the woman to potential risks associated with estrogen-containing contraceptives. Visualizing the cervix and determining the size and direction of the uterus can be challenging in severely obese women during insertion of the device. Optimizing equipment by selecting a large speculum or removing the tip of a condom and placing it over the blades of the speculum can help with exposure . Ultrasound may be helpful to guide insertion. (See "Insertion and removal of an intrauterine contraceptive device".)
For women who do not want to use intrauterine contraception, the potentially higher failure rates associated with oral contraceptives, the patch, and ring need to be balanced with the potentially high user failure rates associated with barrier methods. Contraception failure rates among obese oral contraceptive users are probably lower than in obese women using barrier methods, but women who choose to use oral contraceptive pills, the patch, or ring should consider using condoms as well to decrease pregnancy risk and the risk of acquiring sexually transmitted infections, if applicable. In our opinion, the decision to use the pill, patch or ring should be based on the mode of hormonal delivery that the patient feels fits with her lifestyle. For all women who want to use a pill, we start with a pill containing 20 to 30 mcg of ethinyl estradiol. Although insufficient evidence exists to recommend a specific estrogen dose or use of a higher rather than a lower dose oral contraceptive pill, most pharmacokinetic studies in obese women used a pill containing 20 mcg ethinyl estradiol. We do not start any women on a pill with more than 35 mcg of ethinyl estradiol. If obese women are satisfied with a particular pill formulation, we do not switch them to a different pill unless they develop contraindications to estrogen use, in which case we discuss non-estrogen contraceptive options. Although it is tempting to simply double the dose of oral contraceptive used by obese women to achieve higher serum levels, alterations in the pharmacokinetics of steroid hormones based on weight and resulting end-organ suppression (prevention of ovulation) do not have linear relationships. Furthermore, doubling the dose could increase side effects and risks, so this is not recommended.
Because obese women, especially those with comorbidities, are at higher risk of pregnancy-related complications, avoidance of unintended pregnancy is especially important. In addition, obesity is a risk factor for endometrial hyperplasia and endometrial cancer. Both types of IUD  and hormonal contraceptives provide endometrial protection and have been associated with a decrease in this risk. (See "Endometrial carcinoma: Epidemiology and risk factors", section on 'Hormonal contraceptives'.)