Hormonal birth control does not induce VTE recurrence

Hormonal contraceptives don’t appear to increase the risk of recurrence of venous thromboembolism among women taking anticoagulants, according to a report published in Blood.

Clinicians are often reluctant to prescribe hormonal contraceptives for women who develop venous thromboembolism (VTE) because the drugs are known to raise the risk of VTE and are considered to be contraindicated in either active or previous VTE. But effective contraception is necessary for women of childbearing age who are taking anticoagulants, because these drugs cross the placenta and could cause fetal bleeding and other adverse events, wrote the A. Bianchi Bonomi Hemophilia and Thrombosis Center, Fondazione IRCCS Ca’ Granda-Ospedale Maggiore Policlinico, Milan.

Adding further to the confusion, World Health Organization guidelines state that estrogen-containing contraceptives confer “an unacceptable health risk” during anticoagulant therapy for VTE, but the International Society on Thrombosis and Haemostasis recommends that women diagnosed with VTE continue oral contraceptive and estrogen-replacement hormonal therapy until they discontinue anticoagulant therapy “because any prothrombotic effect of hormonal therapy is likely to be suppressed by therapeutic intensity anticoagulation.”

In the current study, the investigators performed a secondary analysis of data accrued in two large trials evaluating rivaroxaban versus enoxaparin plus vitamin K antagonists, which involved 1,888 women younger than age 60 (mean age, 41 years) who were being treated for acute deep vein thrombosis or acute pulmonary embolism. A total of 402 of these women used hormonal therapy during the four-year studies.

There were 7 VTE recurrences during hormonal contraceptive use and 38 without hormonal contraceptive use. The incidence densities were 3.7 percent per year with hormonal therapy and 4.7 percent per year without it, for a hazard ratio of 0.56.

This indicates that hormonal contraceptive use did not make a clinically important difference in the rate of VTE recurrence. Moreover, these findings were consistent regardless of whether the contraceptives contained estrogen or progestin only, and remained consistent in sensitivity analyses.

“These results challenge the WHO guidelines and instead support the International Society on Thrombosis and Haemostasis recommendations,” the investigators wrote. 

“Our finding of similar risks of recurrent VTE of women who did or did not receive hormonal therapy, whether progestin-only or estrogen-containing therapy, supports a treatment selection that incorporates patient preference, including the choice of estrogen-containing contraception.”