Combined oral contraceptives increase risk of blood clots in women with PCOS

Women with polycystic ovary syndrome (PCOS) who are taking combined oral contraceptives have a 2-fold risk of blood clots compared with women without the disorder who take contraceptives, states a study published in CMAJ (Canadian Medical Association Journal).

PCOS affects between 6% and 10% of women of reproductive age with some estimates as high as 15%, making it the most common endocrine disorder in this age group. Risk factors for heart disease such as hypertension, diabetes, obesity and others are double among women with PCOS compared with women without the disorder. It is usually treated with combined oral contraceptives to regulate menstrual cycles and to help with acne and excessive hair growth associated with the condition. However, combined oral contraceptives are known to increase the risk of cardiovascular events.

Researchers from the US and Canada looked at 87 012 women aged 18 to 46 years in the US, half with PCOS and half as controls, to determine whether women with PCOS taking birth control pills are at increased risk of venous thromboembolism compared to matched contraceptive users. They excluded women with a history of heart disease, cancer and previous blood clots.

"We found a 2-fold increased risk of venous thromboembolism among women with PCOS taking combined oral contraceptives compared with matched controls," states Steven Bird, lead author and pharmacoepidemiologist with the Food and Drug Administration (FDA) in the United States, with coauthors. "We found a similar increased risk when we expanded the definition of PCOS by including its symptoms and treatment. We also found a 1.5-fold increased relative risk of venous thromboembolism among women with PCOS who were not taking contraceptives compared with matched controls."

"Our findings are consistent with the previously reported 2-fold increase in most of the risk factors for venous thromboembolism among women with PCOS."

"Physicians should consider the increased risk of venous thromboembolism when prescribing contraceptive therapy to women with PCOS," conclude the authors.