The risk of venous thromboembolism (VTE) after induced abortion is higher than in nonpregnant women but lower than after live birth, Canadian researchers report

To address this issue, Dr. Ray's team used Ontario province data to assess the risk of VTE within 42 days of an induced abortion among 176,001 women pregnant for the first time, compared with 880,005 women who had never been pregnant and 176,001 women who delivered a newborn baby after their first pregnancy.

The VTE rate in the induced abortion group was 30.1 per 100,000 women, compared with 13.5 per 100,000 nonpregnant women and 184.7 per 100,000 women after live birth, according to the June 8th Lancet Haematology online report.

Compared to the risk in the nonpregnant group, the risk of VTE was 2.23-fold higher in the induced abortion group and 13.7-fold higher in the live birth group. The risk was 84% lower in the induced abortion group than in the live birth group. The VTE risk after an induced abortion was similar to that of an ongoing pregnancy from the same gestational age onward.

Rate of VTE

Among women with induced abortion, the rate of VTE was higher when the abortion was done in a hospital setting, was performed at 15 weeks' gestation or later (compared with earlier), when women were 35 years old or older, and among women with comorbidities.

"This study was conducted in a setting where over 95% of the induced abortions are performed surgically," he said. "Future investigation should compare the risk of VTE following surgical versus pharmaceutical-induced abortion."

"Guidelines about the prevention of pregnancy-related venous thromboembolism cannot simply be translated to women having an induced abortion, because the risk-to-benefit ratio of postpartum prophylaxis is different, with a much higher number needed to treat to prevent one venous thromboembolic event," they note.

"Epidemiological studies are a crucial step towards evidence-based guidance for tackling a frequent clinical question such as the need for prophylaxis of venous thromboembolism after induced abortion."

Dr. Kelley McLean, who recently reviewed the diagnosis and management of VTE in pregnancy, said "These findings are of substantial importance in the context of post-abortion contraception counseling. The CDC's 2016 Medical Eligibility Criteria for Contraceptive Use makes no reference to the possibility of increased VTE risk post-abortion, and combined oral contraceptives are given Category 1 status after both 1st and 2nd-trimester abortions."

"This is in contrast to the Category 4 status ('unacceptable health risk') for the first 21 days postpartum and Category 3 between 21 and 42 days after delivering an infant," she said. "Additionally, these findings highlight the importance of considering pharmacologic thromboprophylaxis in women with prior VTE or with high-risk thrombophilia, and make future studies in these high-risk sub-groups of paramount importance."

"The findings should prompt careful consideration of postabortal contraceptive choices, and patient education and counseling should include a VTE risk discussion, particularly in the context of estrogen-containing contraceptive choices," Dr. McLean said.

"We know that LARC is highly effective, and is often the safest choice for many women," she added. "This may be particularly true for women who are within 42 days of an abortion procedure, and for women who have chosen to initiate contraception after an abortion, the relative safety of LARC compared with estrogen-containing contraceptives in terms of VTE risk should be presented."