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The prevalence of obesity in the United States has increased dramatically over the past four decades. In 2014, about 37% of U.S. women ages 20-39 were obese, which is defined as a body mass index of 30 or greater.
Results of just-released research indicate that obese women are more likely to rely on female sterilization than on other forms of contraception.1 How do weight concerns and obesity affect contraceptive decision-making?
Increased weight and obesity are increasingly common among people of reproductive age in the United States, says William Mosher, PhD, Senior Scientist in the Johns Hopkins University Bloomberg School of Public Health in Baltimore.
“Obesity is known to worsen pregnancy risks and complications, such as gestational diabetes, pre-eclampsia, gestational hypertension, cesarean birth, preterm birth, congenital anomalies, and perinatal death, according to recent reviews, so the health consequences of unintended pregnancy among obese mothers may be more serious than among those with normal body mass index [BMI, defined as weight in kilograms divided by height in meters squared],” notes Mosher, who served as lead author of the research paper. “This makes their contraceptive choices interesting and important for their own health and the health of their babies.”
To conduct the analysis, researchers looked at the 2011-2015 National Survey of Family Growth (NSFG), a large nationally representative survey with data on BMI, contraceptive use, and the necessary control variables. These data allowed researchers to look at obese women’s use of female sterilization, the intrauterine device (IUD), and systemic hormonal contraception (oral contraceptive pills and other hormonal options), Mosher explains.
“We found that obese women are much more likely to choose female sterilization, somewhat more likely to use the IUD, and less likely to use hormonal contraception, than women with normal BMI (less than 25), even after controlling for age, parity, education, race, marital status, and self-reported health,” states Mosher. “The use of sterilization is still very common among obese women, and the use of IUDs is still lower than it could be.”
As the article suggests, Mosher says this finding could reflect a need for certainty that protection from pregnancy is permanent, less access to IUDs or less knowledge of their effectiveness, a wish to avoid any more use of the Pill or other systemic hormonal contraception, a fear that health insurance may not be available in the future and therefore a permanent solution (sterilization) is needed, or other factors not currently understood.
The prevalence of obesity in the United States has increased dramatically over the past four decades. From 1988-1994, 25.9% of women age 20 years and older were considered obese (defined as a BMI of 30 or above), with 3.9% considered extremely obese (Class 3 obesity defined as BMI of 40 or above). In 2013-2014, in this same age group, 40.4% were classified as obese and 9.9% were classified as extremely obese.2
While no evidence suggests that any contraceptive method is ineffective in obese adolescents or women, concerns have been raised about the diminished effectiveness of certain methods because of physiologic differences in women who are obese.3 Such concerns center on methods with a mechanism of action that relies on the systemic distribution of steroid hormones. These include contraceptive pills, the patch, and the vaginal ring.
Studies of the combined oral contraceptive have indicated altered contraceptive steroid half-life in obese women,4-5 although follicular development did not suggest significant difference in obese vs. normal-weight women who used the Pill.4-6 In a large prospective postmarketing study of more than 52,000 women, data indicated a slight increased risk of failure (hazard ratio, 1.5; confidence interval [CI] 1.3-1.8) in obese women compared with normal-weight women.7
Labeling for the contraceptive patch package states that it may be less effective in women weighing more than 90 kilograms. In two small studies of the vaginal ring, follicular development was founded to be minimal in obese women, and hormone levels remained in the therapeutic range up to 35 days after ring insertion.8-9
While a 2009 review of available data did not find evidence of lower combined hormonal contraceptive effectiveness in obese women, it noted major limitations of available retrospective data, much of which relied on self-reporting of compliance and body weight.10 A 2013 Cochrane review and 2016 update concluded that available evidence generally did not indicate an association between BMI or weight and contraceptive effectiveness. However, the analyses noted that while more recent studies included larger numbers of overweight and obese women, the overall quality of evidence was low, particularly for older studies.11,12
Obtaining prospective data in broadly representative populations with respect to BMI is “critically important,” as obesity rates continue to rise among U.S. women, states a recent commentary on the subject.13 Emerging prospective data from contraceptive trials suggest that rising rates of obesity in the U.S. population may be an important contributor to the “creeping Pearl” phenomenon. The Pearl Index is defined as the number of pregnancies observed in a trial, divided by the number of cycles of product use multiplied by 1,300.13
According to the U.S. Selected Practice Recommendations for Contraceptive Use, obese women generally can use combined hormonal contraceptives (U.S. MEC 2; [benefits outweigh theoretical or proven risks]).14,15 Screening for obesity is not necessary for the safe initiation of combined hormonal contraceptives. Clinicians may wish to measure weight and calculate BMI at baseline to help monitor any changes and counsel women who might be concerned about weight change perceived to be associated with their contraceptive method.
Although not directly studied, BMI should not have an effect on the effectiveness of the copper or hormonal IUD, since the contraceptive effect is local. Studies also note the efficacy of the etonogestrel implant does not appear to be affected by weight.3 Research suggests the efficacy of the contraceptive injection is not decreased in obese women.3 Women with a body mass index of 30 or higher can safely use all three methods, as all are rated Category 1 (no restrictions on use).
Financial Disclosure: Consulting Editor Robert A. Hatcher, MD, MPH, Nurse Planner Melanie Deal, MS, WHNP-BC, FNP-BC, Author Rebecca Bowers, Executive Editor Shelly Morrow Mark, Copy Editor Savannah Zeches, and Editorial Group Manager Terrey L. Hatcher report no consultant, stockholder, speaker’s bureau, research, or other financial relationships with companies having ties to this field of study.