Being overweight or obese is a reality for more than two-thirds of American adults. Women of color, women who live in poverty, and those who live in certain geographic regions are at increased risk of being overweight or obese, but this chronic health condition can affect anyone.
Slightly more than one-half of pregnancies in the United States are unintended, and being overweight or obese is associated with a higher risk of unintended pregnancy. Therefore, if you are overweight or obese, it's important to find an effective birth control method.
Read on to learn what you need to know about birth control options and effectiveness when you are overweight or obese.
What Is BMI?
In a clinical setting, your body mass index (BMI) is used to determine whether you're considered overweight or obese. If your BMI is between 25 and 29.9, you are in the “overweight” category. If your BMI is over 30, you are in the “obese” category. Your doctor or nurse practitioner can help you calculate your BMI, or you can do it yourself online with HealthCentral’s body mass index calculator.
When making recommendations for birth control for women with a BMI over 25, many doctors have relied on low quality studies or been ill informed. This may have led to misinformation about effective birth control in overweight and obese women, leaving them at risk of unwanted pregnancies.
Birth Control and Weight Gain
Some women who are overweight or obese may be hesitant to take birth control because they have heard weight gain can be a side effect. However, numerous studies have been done on different birth control methods that show the weight gain associated with each method is roughly equivalent to the normal weight gain associated with aging.
How Well Do Different Birth Control Methods Work if You’re Overweight?
One of the biggest concerns regarding birth control in overweight and obese women is the question: Is it still effective? To address this question, first you have to understand how the earliest birth control studies were done: Often, resaerchers left out overweight and obese women when doing trials on efficacy. This means that there may be less data available on how well birth control works in these women. That said, rather than making blanket statements, it's important to look at birth control effectiveness method by method.
The Intrauterine Device
The IUD should work the same regardless of your body type and weight. The failure rate for the IUD in overweight and obese women is 1 in 100.
One issue to keep in mind is that the IUD may be more difficult to insert in women who are overweight, depending on the skill of the practitioner and their experience dealing with bigger bodies in general. Some have suggested that an ultrasound can help in IUD placement if it is difficult.
The birth control implant, which release the hormone progestin into the body, is also effective at preventing pregnancy in overweight and obese women. While one study showed there was less of the hormone in the blood of these women than in women of normal weight, the amount was still enough to prevent ovulation and, therefore, provided protection against pregnancy.
One study even concluded that the implant may be considered as a first-line birth control method for any woman, including those above normal weight.
Depot medroxyprogesterone acetate (DMPA) is a birth control injection given every three months. While one study found the amounts of hormones detected in the blood stream varied by BMI, the rates of pregnancy remained the same in all weight categories, including those with a BMI over 40. The only special consideration for women who are overweight is that longer needles may need to be used, depending on the amount of body fat at the injection site.
The Patch and the Ring
Studies done on the birth control patch and ring also show no increased risk of pregnancy in women with a BMI of over 25. In blood tests, researchers found a lower concentration of ethinyl estrogen from the birth control in these women, but not enough to decrease the protection against pregnancy.
While this difference in the estrogen levels may help explain why overweight or obese women can experience more spotting with these methods, the patch or ring may still be used to prevent pregnancy in women of any weight.
Birth Control Pills
There are many types of birth control pills available, including pills with estrogen and progestin (combination pills) and pills with just progestin, not to mention a variety of strengths of each. Depending on the specific pill, there may be different risks and benefits for you to consider; therefore, it’s important to talk to your doctor about what pill may work best for you if you above normal weight.
One study did look at the hormone levels in obese women taking birth control pills, and, like with the implant, there was a lower amount found in the blood of obese women, but there weren't signs of increased ovulation.
However, the study did note that it may take longer for the pill to be effective in women with a higher BMI — meaning that once you start the pill, you’d need to give it more time to work while you used a backup method of contraception.
Another study looked at whether women could potentially skip the placebo days (typically the last pills in a monthly pack that don’t contain any hormones and allow you to have a period) and immediately start the next pack to avoid the potential of a slower return to efficacy of the hormones as they were reintroduced.
This is something many pill users already do — skip the placebo pills to stay period free. Therefore, this study showed that doing so did not increase pregnancy rates and is a possibility for women who wish to use birth control this way.
The biggest risk of combination pills is the increased risk of blood clots. The overall risk of having a blood clot due to birth control pill use is very small, but it is, according to some sources, higher in women who have a BMI higher than 25. According to one study, BMI over 25 left to about an additional 5-10 events per 10,000 people per year.
This is not considered risky enough by most practitioners to not recommend combined oral contraceptives at all. In fact, the risk of blood clots in overweight or obese women who are pregnant is much higher, making pregnancy much riskier than taking birth control pills in terms of blood clots.
The World Health Organization (WHO) cites no safety concerns for birth control pills.
The Bottom Line
While new studies are more likely to include women with a BMI higher than 25, according to the Cochrane Database of Systematic Reviews, there is still not a ton of great evidence that there are actually increased risks with birth control in an obese population. Generally, however, there does not seem to be an association with BMI and a higher birth control failure rate.
In the end, the best birth control method is the one that you will actually use — and use correctly. This has been shown time and time again to be the biggest factor in whether a birth control method works.
Be sure to discuss you concerns with your practitioner about the safety and effectiveness of your birth control method. Include in this discussion a look at your medical history and things that may make your individual choice different.