When Birth Control Fails

Fat and Contraception Effectiveness

February 1, 2018

The most critical element in preventing unplanned pregnancies is that the usage of safe and effective contraception by girls who don’t want to conceive. Yet almost half of all unintended pregnancies occur in women who report using contraception during the month they that conceived.

One of the issues that might be leading to birth control failure is that a woman’s weight.

Obese women may not understand that their weight could be undermining the effectiveness of the contraceptive method.

Obesity rates have increased over the last two decades and continue to be a public health concern in the United States and around the world. Obesity is defined as a body mass index (BMI) of 30 or higher, whereas an obese person has a BMI of 25 to 29.9. BMI is calculated from a person’s height and weight and offers a reasonable indicator of body fatness and weight classes which may lead to health problems.

Unfortunately, contraceptive research has not included obese and obese women in clinical trials. This has resulted in a restricted body of data regarding health efficacy and safety in obese and overweight women. That’s unfortunate, given that successful contraception is even more important for fat women given the truth their higher risk of pregnancy-related complications.

To gain a greater understanding of how contraceptive effectiveness can be reduced by obesity, I researched an article on UpToDate — a trusted digital reference used by many doctors and patients:

“Many metabolic processes are affected by adiposity, and such changes in metabolism could potentially impact contraceptive efficacy.

Since changes in metabolism are more contingent upon adiposity than on body proportions (ie, body mass index [BMI]), weight is likely more applicable than BMI in determining variability in contraceptive efficiency. Higher weight interferes with the increased metabolic rate. Specifically, the clearance of hepatically metabolized medications, for example contraceptive steroids, increases with increasing body weight. Theoretically, the half life of those drugs might be shorter in obese girls and serum levels may be inadequate to keep up a contraceptive effect. Additionally, obese women have a larger circulating blood volume compared to normal weight women. This may cause substantial dilution of the concentration of contraceptive steroids, thereby decreasing contraceptive efficacy. What’s more, contraceptive steroids are absorbed by adipose tissue, so women with more cerebral might have less steroid accessible to circulate.

“According to the potential effects of obesity on the pharmacokinetics of contraceptive steroids, it is tempting to simply recommend decreasing the dose of contraceptive pills used by obese women. But, side effects and dangers would also rise. As an example, a higher dose of estrogen containing contraceptives would increase the risk of deep venous thrombosis and would be compounded by the danger already present for fat women.”

Therefore, what exactly does this imply? Let us break down this significant details.

Metabolic processes are biological processes that a living cell or organism utilizes to give energy necessary for growth and life. Metabolism describes the chemical reactions in the human body cells which convert the fuel from food into the energy that our bodies will need to function. Individuals with higher weights (because of an excessive amount of body fat) appear to have higher metabolic prices. Hepatically metabolized medications, such as hormonal contraceptives, are absorbed by the digestive tract and reach the liver prior to the rest of the human body. The liver then metabolizes the drug, so that the concentration of the medication is greatly decreased by the time it enters the circulatory system.

Overweight women may also be more likely to have high levels of enzymes from the liver which will break down the hormones faster. Therefore, as there is more tissue by which blood must circulate, the amounts of circulating hormones may be diminished. This number may not contain concentrations high enough to give pregnancy protection (i.e., prevent ovulation, thicken cervical mucus, or thin the uterine lining).

Additionally, the half-life of a drug (basically, how much time it takes for half of it to be eliminated from the bloodstream) may be briefer for overweight women because it’s summoned faster — thus, there may not be sufficient contraceptive hormone left in the human body to have a contraceptive effect.

Another factor has to do with blood circulation. So as to be effective, contraceptive hormones will need to circulate through a woman’s bloodstream. If a girl has a bigger body mass, then it might be more difficult for sufficient circulation to happen, because of higher amounts of blood circulating around the bodies. As a result of comparatively low hormone levels in childbirth, the larger blood volume could thin out the hormones and make them less effective.

Complicating the circumstance, estrogen and progestin are stored in adipose tissue. The more fat cells that a woman gets, the greater the odds that the hormones will become trapped in the fat rather than flowing through the bloodstream.

Due to the way an overweight woman’s body may absorb, distribute, metabolize and remove hormonal imbalances, there are people who assert that contraceptive effectiveness can be maintained if the hormonal amount in the contraceptive is doubled. This poses a problem, however, because of potential side effects. Adding higher doses of estrogen in childbirth could raise the risk for developing unwanted effects such as deep venous thrombosis (blood clots), stroke, obesity, high blood pressure or heart attacks — risks already associated with obesity.

So in regards to weight and birth control effectiveness, it’s always important to evaluate the risks of unintended pregnancy against the benefits and disadvantages associated with a specific contraceptive method. In general, methods, in which contraceptive failure is more likely to happen in obese women than in women of normal weight, include: oral contraceptives, the contraceptive patch, and Implanon/Nexplanon.

  • Weight and Birth Control Pill Effectiveness

For obese girls, IUDs and surgical sterilization might be more effective contraceptive procedures. However, because of the increased body mass, these processes may be more difficult to finish.

Other methods not influenced by fat are hysteroscopic sterilization (Essure) and barrier methods such as condoms, female condoms, the sponge, diaphragms and cervical caps.

  • Powerful Birth Control Strategies for Overweight Women

Want to discover more? See UpToDate’s subject,”Contraception counseling for overweight women,” for additional in-depth medical information on counseling obese girls about their contraceptive choices and exploring how weight can contribute to contraceptive failure.