Glasier A, Cameron S, Blithe D, et al. Can we identify women at risk of pregnancy despite using emergency contraception? Data from randomized trials of ulipristal acetate and levonorgestrel [published online ahead of print April 2, 2011]. Contraception. doi:10.1016/j.contraception.2011.02.009.
Edelman AB, Carlson NE, Cherala G, et al. Impact of obesity on oral contraceptive pharmacokinetics and hypothalamic-pituitary-ovarian activity. Contraception. 2009;80(2):119–127.
Westhoff CT, Torgal AL, Mayeda ER, et al. Ovarian suppression in normal-weight and obese women during oral contraceptive use. Obstet Gynecol. 2010;116(2 pt 2):275–283.
As we observed, despite more widespread use of EC after the LNG-only method was made available without a prescription, we have not realized the public health benefit of a decreased rate of unintended pregnancy or abortion.4 Studies have shown that, despite taking EC, women who have further acts of intercourse in the same cycle of EC use are more likely to conceive.12,13
We now have clear information about another specific population in which EC is more likely to fail: overweight and obese women. Compared with women of normal weight (body mass index [BMI] <25), overweight women (BMI 25–30) had a risk of pregnancy 1.5 times greater, and obese women (BMI ≥30) had a risk of pregnancy more than three times greater.13
Pregnancy rate among obese women using LNG was the same as the background rate
Obese women who used LNG as EC had a pregnancy rate of 5.8%, which is approximately equivalent to the overall pregnancy rate expected in the absence of EC. Overweight women in the LNG group had a relative risk of pregnancy that was double that of normal or underweight women, whereas overweight women taking UPA had the same risk as normal or underweight women taking the same medication.
When researchers compared pregnancy rates by weight instead of BMI, differences persisted between the two treatment options, with a limit of efficacy reached at a weight of 70 kg (154 lb) for LNG, compared with 88 kg (194 lb) for UPA.
OC hormone absorption is slower in obesity
Two recent studies—by Edelman and colleagues and Westhoff and coworkers—have demonstrated that OC hormone absorption is slower in obese women than it is in women of normal weight. With EC, immediate absorption is important; this delay could explain the lower efficacy in obese women. No studies have evaluated whether a higher or double dose of LNG would improve efficacy. Like women who experience repeated acts of unprotected intercourse, overweight and obese women are at high risk of EC failure and should be counseled about this risk.
As the incidence of obesity continues to increase exponentially in the United States, the efficacy of our commonly used methods of EC will continue to decline. At a minimum, overweight and obese women should be counseled to take UPA rather than LNG because of its increased efficacy in this population. We also need to inform overweight patients that their risk of pregnancy is higher than is commonly quoted.
Have we overlooked the best available emergency contraceptive?
Wu S, Godfrey EM, Wojdyla D, et al. Copper T380A intrauterine device for emergency contraception: a prospective, multicentre, cohort clinical trial. BJOG. 2010;117(10):1205–1210.
Turok D, Gurtcheff S, Handley E, et al. A pilot study of the Copper T380A IUD and levonorgestral for emergency contraception. Contraception. 2010;82(6):520–525.
The copper IUD has always been the most effective EC available. Not only does it prevent pregnancy when inserted as EC, but it continues to provide long-term, reversible contraception for 10 years or longer. Two large studies—one of them published within the past year—found efficacy rates of 96.9% and 100%, much higher than those associated with oral EC, with only two pregnancies occurring in more than 2,000 women.14,15
Although use of the IUD as EC was described as early as 1976, adoption of this method has been minimal in the United States.16 One reason may be the need for a clinician to insert the device, but many providers undoubtedly dismiss the IUD as an option for EC, believing that American women are unwilling to accept it. Some providers maintain the longstanding opinion that the IUD is an option only for parous women, although this notion has been cast aside by layers of medical evidence, as reviewed by current Centers for Disease Control and Prevention (CDC) medical eligibility criteria for contraception.17
All women should be counseled about the long-term benefits of the copper IUD, the most reliable method of EC. The copper IUD not only provides effective emergency contraception but also long-term contraception for 10 years or more. Therefore, we should offer the copper IUD as first-line treatment for women seeking EC (FIGURE). This method is likely to be much more acceptable to patients than previously assumed.