Birth control pills are the leading method of birth control in the United States. Birth control pills increase the chance of developing a blood clot by about three- to four-fold. This increase is a result of estrogen (most birth control pills contain estrogen and synthetic progesterone), which increases the levels of clotting factors in the body.
The average risk of developing a blood clot is still small. Only one in 3000 women per year who are taking birth control pills will develop a blood clot. For some women, the risk is much higher. Women with a history of thrombosis are not recommended to take birth control pills for this reason.
New research published by the journal ESC Heart Failure is shedding light on the additional risk to obese women of taking birth control pills. Specifically, combined oral contraceptives (COCs), or birth control pills that contain estrogen and synthetic progesterone. Women who are obese and use combined oral contraceptives have between 12- to 24- fold increase in their chance of developing a blood clot.
The researchers noted that progestin-only products are a safer alternative in patients who are overweight or obese. Study author Professor Giuseppe Rosano says that “the scientific evidence indicates that obesity and combined oral contraceptives have a synergistic effect on VTE (blood clot) risk and this should be considered in prescribing decisions. Progestin-only products, including pills, intrauterine devices, or implants are a safer alternative to the combined pill in women carrying excess weight.”
These results are critical in informing public health decisions. Those at a higher risk of experiencing negative side effects from birth control pills that contain estrogen should be advised to use safer alternatives such as progestin-only products, non-hormonal intrauterine devices, or implants that do not contain estrogen.
“Obese women taking contraceptives are vulnerable to VTE and should take steps to limit their other predisposing factors for cardiovascular disease, for example by quitting smoking and increasing their physical activity levels,” adds Professor Giuseppe Rosano.
