Results of a new statistical analysis of clinical data suggest a significant drop in the efficacy of levonorgestrel emergency contraceptive pills (ECPs) with increasing body weight.
• Questions of whether body mass index (BMI) or weight might influence the efficacy of ECPs first were raised when findings from a 2011 analysis indicated that levonorgestrel, when taken for emergency contraception among overweight or obese women, had decreased efficacy in preventing pregnancy.
• Researchers pooled data from two large, multicenter, randomized controlled trials designed to assess emergency contraceptive efficacy to evaluate the effect of weight and BMI on pregnancy rates among women who received such pills. For women weighing more than 75 kg (165 pounds), levonorgestrel ECPs were minimally effective.
Results of a new statistical analysis of clinical data suggest a significant drop in the efficacy of levonorgestrel emergency contraception (EC) with increasing body weight.1
Questions of whether body mass index (BMI) or weight might influence the efficacy of EC first were raised when findings from a 2011 analysis indicated that levonorgestrel, when taken for emergency contraception among overweight or obese women, had decreased efficacy in preventing pregnancy.2 (Contraceptive Technology Update reported on the data in the article, “Hope vs. reality — Access to EC pills doesn’t work,” January 2013, p. 8.)
To further evaluate the effect of weight and BMI on the efficacy of levonorgestrel emergency contraception, researchers pooled data from two large, multicenter, randomized controlled trials designed to assess emergency contraceptive efficacy to evaluate the effect of weight and BMI on pregnancy rates among women who received levonorgestrel.3,4
The researchers used descriptive methods, such as comparing means and distributions according to pregnancy status and pregnancy rates across weight and BMI categories, as well as cubic spline modeling, to describe the relationship between pregnancy risk and weight/BMI. Cubic spline modeling utilizes five predictions of the pregnancy rates corresponding to five percentiles (the first, third, fifth, seventh, and ninth deciles) of the distribution of the data.
A total of 1,731 women were in the analysis population, and 38 pregnancies were reported. Women for whom levonorgestrel was not effective in preventing pregnancy had a significantly higher mean body weight and BMI than women who did not become pregnant (76.7 versus 66.4 kg, p less than .0001; 28.1 versus 24.6 kg/m2, p less than .0001).
The estimated pregnancy rate increased significantly from 1.4% (95% confidence interval [CI]: 0.5%-3.0%) among the group of women weighing 65-75 kg to 6.4% (95% CI: 3.1%-11.5%) and 5.7% (95% CI: 2.9%-10.0%) in the 75-85 kg and above-85 kg groups, respectively, findings indicate. Statistical modeling demonstrated a steep increase in pregnancy risk starting from a weight near 70-75 kg to reach a risk of pregnancy of 6% or greater around 80 kg. Similar results were obtained for statistical modeling of BMI, as well as when the two studies were analyzed individually, researchers report.3
How to proceed?
Clinicians need to take into consideration such data when talking with women about emergency contraception. Why? The average U.S. woman now weighs 75 kg (165 pounds).5
Levonorgestrel emergency contraceptive pills are approved for unrestricted sales on store shelves. They include Plan B One-Step (Teva Women’s Health, North Wales, PA); Take Action (Teva), Next Choice One Dose (Actavis, Parsippany, PA), My Way (Gavis Pharmaceuticals, Somerset, NJ), Levonorgestrel 0.75 mg tablets (Perrigo, Allegan, MI), and AfterPill (Syzygy Healthcare Solutions, Westport, CT).
Publication of the new analysis will spread enthusiasm for ulipristal acetate, because most clinics are not able to provide copper IUDs for emergency contraception, says Anita Nelson, MD, professor in the Obstetrics and Gynecology Department at the David Geffen School of Medicine at the University of California in Los Angeles.
Study findings suggest that ulipristal acetate (ella, Afaxys, Charleston, SC) also is impacted by weight. It appears to lose effectiveness at a higher BMI threshold of 35.2,6 Ulipristal acetate is available by prescription only in the United States; it was approved in January 2015 for pharmacy over-the counter sales by the European Commission.
Robert Hatcher, MD, MPH, professor emeritus of gynecology and obstetrics at Emory University School of Medicine in Atlanta, points to the book Managing Contraception 2015-2016, which summarizes the loss of effectiveness of emergency contraceptive pills in overweight women with two concise statements:
• “Emergency contraception with progestin-only pills (e.g. Plan B) is virtually useless with women with a BMI of 36 or greater.”
• “Emergency contraception with ella is useless (ineffective) in women with a BMI of 35 or greater.”7
The copper intrauterine device (IUD) is the most effective form of emergency contraception. It can be inserted up to five days after unprotected intercourse, which reduces the risk of pregnancy by 99%. It retains full efficacy over time and with obesity, and it provides ongoing contraception for up to 12 years.8
Clinicians also might want to consider a recently published commentary that calls for changes in patient counseling for emergency contraception, because typical counseling doesn’t take into account the relative effectiveness of available methods or patient characteristics such as BMI.9 (For more information on tiered counseling, see “It’s time for a tiered approach to counseling on emergency contraception,” CTU)
- Kapp N, Abitbol JL, Mathé H, et al. Effect of body weight and BMI on the efficacy of levonorgestrel emergency contraception. Contraception 2015; 91(2):97-104.
- Glasier A, Cameron ST, 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. Contraception 2011; 84(4):363-367.
- Creinin MD, Schlaff W, Archer DF, et al. Progesterone receptor modulator for emergency contraception. A randomized controlled trial. Obstet Gynecol 2006; 108(5):1089-1097.
- Glasier AF, Cameron ST, Fine PM, et al. Ulipristal acetate versus levonorgestrel for emergency contraception: A randomised non-inferiority trial and meta-analysis. Lancet 2010; 375:555-562.
- McDowell MA, Fryar CD, Ogden CL, et al. Anthropometric reference data for children and adults: United States, 2003–2006. Hyattsville, MD: National Center for Health Statistics. Accessed at http://1.usa.gov/XnlZ7o.
- Moreau C, Trussell J. Results from pooled Phase III studies of ulipristal acetate for emergency contraception. Contraception 2012; 86:673-680.
- Zieman M, Hatcher RA, Allen AZ. Managing Contraception 2015-2016. Atlanta: Bridging the Gap Communications; 2015.
- Reproductive Health Access Project. Emergency contraception: Timing, weight, and efficacy. November 2013. Accessed at http://bit.ly/18GsqnV.
- Thompson K, Belden P. Counseling for emergency contraception: Time for a tiered approach. Contraception 2014; 90(6):559-561.