The prevalence of obesity is increasing in children, adolescents, and adults in developed countries worldwide. In the United States, it is estimated that more than one-third of adults are obese . The personal and societal costs of obesity are significant since obesity is associated with an increased risk of several medical disorders and pregnancy complications . (See "Health hazards associated with obesity in adults" and "The impact of obesity on female fertility and pregnancy".)
Use of safe and effective contraception by women not wishing to conceive is of the utmost importance for preventing unintended pregnancy. Because women with chronic conditions like obesity are at higher risk of pregnancy-related complications, proper contraceptive use and avoidance of unintended pregnancy are especially important in this population. In addition, some contraceptive methods offer noncontraceptive medical benefits, such as reduction in risk of endometrial and ovarian cancer and decreased menstrual bleeding. Nevertheless, one study reported that obese sexually active women were more likely to report contraceptive nonuse than normal weight women . Of note, obesity is not significantly associated with sexual orientation, age at first intercourse, frequency of heterosexual intercourse, or the number of lifetime or current male partners .
Counseling obese women about their contraceptive options can be challenging. Historically, contraceptive research has excluded obese and overweight women from clinical trials resulting in a limited body of evidence regarding contraceptive effectiveness and safety in obese and overweight women [2,5].
It is important to explore all of the factors that can contribute to contraceptive failure, not just the effect of weight, since approximately one-half of all pregnancies are unintended and one-half of these occur in women using some form of contraception . In large groups of women, the overall rate of contraceptive failure is related to the inherent effectiveness of the method, compliance, fecundity of the population, and sexual behavior (eg, rare versus frequent sexual intercourse). There is no evidence that obesity affects compliance  or frequency of sexual intercourse . Obesity can affect fecundity, but the majority of obese women ovulate regularly. There is some evidence that, compared to normal weight women, the risk of contraceptive failure is higher in obese women using the contraceptive patch [2,8], combined oral contraceptive pills [9,10], and contraceptive implants ; however, the magnitude of excess risk is unclear . However, data from the 2002 National Survey of Family Growth do not support an association between obesity and unintended pregnancy . This makes it difficult to properly inform overweight and obese women of their risk of pregnancy when using hormonal methods.
As a general guideline, the emotional aspects of unintended conception and the health risks of pregnancy should be weighed against the risks and disadvantages associated with a specific contraceptive method and the risk of contraceptive failure.