For women with histories of venous thromboembolism (VTE) who require anticoagulant therapy, choosing appropriate contraception can be challenging. WHO investigators reviewed publications that addressed contraceptive use in women who received anticoagulant therapy for current VTE, those who received such therapy for other indications (e.g., prosthetic heart valves), and those with heavy menstrual bleeding associated with disorders such as von Willebrand disease. Highlights of the WHO observations and recommendations are:

Progestin-only contraceptives do not seem to raise risk for VTE.
Women with histories of VTE who are on anticoagulant therapy should not use estrogen-progestin contraceptives (oral, transdermal, or vaginal ring).
The levonorgestrel-releasing intrauterine device (LNG-IUD) is effective for heavy menstrual bleeding that is associated with anticoagulation or bleeding disorders, and might be safer than surgical treatment.
Suppression of ovulation with depot medroxyprogesterone acetate (DMPA) is effective in preventing recurrent hemorrhage from postovulation cysts.
Insertion of IUDs and contraceptive implants — and deep injections of DMPA — seem to be safe in women receiving anticoagulation therapy who have international normalized ratios (INRs) of 2.0 to 3.0.
Little evidence suggests that hormonal contraceptives interact with anticoagulation therapies, including warfarin. Frequent monitoring of INRs is important when women on anticoagulation therapy begin hormonal contraceptives

Comment: Both pregnancy and use of estrogen-containing contraceptives are associated with excess risk for VTE; moreover, warfarin use is associated with birth defects as well as heavy menstrual bleeding and hemorrhage from postovulatory cysts. Accordingly, effective contraception is important for women with histories of VTE who receive anticoagulant therapy. Because progestin-only ("mini") pills and progestin implants do not predictably diminish heavy menstrual bleeding, these methods are less appropriate than DMPA or the LNG-IUD for anticoagulated women with heavy bleeding Preventing ovulatory hemorrhage in anticoagulated women requires an agent that suppresses ovulation reliably. Hence, DMPA is appropriate in this context, whereas the LNG-IUD, implants, and minipills (which do not consistently prevent ovulation) are not. Consistent with these recommendations, most clinicians are reluctant to prescribe estrogen-containing contraceptives for anticoagulated women. However, no evidence suggests that estrogen-containing contraceptives further raise VTE risk in women who receive warfarin chronically. If patients will not accept or cannot use the LNG-IUD or DMPA in this setting, use of estrogen-progestin pills, patch, or ring (with ongoing INR monitoring) can be considered.

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