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Having an abortion may increase risk for blood clots

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July 3, 2018

Women who recently had abortions had double the risk for venous thromboembolism of women who were not pregnant, study data showed.

However, the risk for VTE among women who had an abortion was significantly lower than that of women whose pregnancies ended in live births.

Venous thromboembolism is a leading cause of maternal morbidity and mortality,” Joel G. Ray, MD, MSc, professor of medicine at University of Toronto, and colleagues wrote.

“Approximately 25% of pregnancies end in induced abortion, accounting for 56 million induced abortions annually worldwide,” he added. “Although information about risk [for] VTE in pregnancy exists, data about the risk after induced abortion is scarce.”

The researchers performed a propensity-matched cohort study, reviewing data from the universal health care system in Ontario, Canada. Ray and colleagues matched primigravid women aged 15 to 49 years who had abortions between 2003 and 2015 (n = 176,001) with primigravid women who had live births (n = 176,001) and nonpregnant women (n = 880,005) who did not conceive within a year of their matched counterparts’ abortions.

The main outcome was risk for VTE within 42 days of the index date — defined as the date of abortion, live birth or, in the case of nonpregnant women, the date of a matched pregnant women’s abortion.

The rate of VTE within 42 days was 30.1 (95% CI, 22-38.2) per 100,000 among women who had an abortion, compared with 13.5 (95% CI, 11.1-16) per 100,000 among nonpregnant women.

However, women who had abortions had a significantly lower risk for VTE within 42 days than those whose pregnancies ended in live births, whose rate of VTE within 42 days was 184.7 (95% CI, 164.6-204.7) per 100,000 (HR = 0.16; 95% CI, 0.12-0.22).

“For clinicians and patients, it is important to acknowledge that the risk of venous thromboembolism after induced abortion is higher than in nonpregnant women, which should lower the index of suspicion in women who present with signs or symptoms of deep vein thrombosis or pulmonary embolism,” Saskia Middeldorp, MD, PhD, professor of medicine, and Willem M. Ankum, MD, PhD, gynecologist, both of Academic Medical Center at University of Amsterdam, wrote in an accompanying editorial.

Middeldorp and Ankum added that the findings raised the question of how abortion impacted risk for women with a history of VTE — a group not included in Ray and colleagues’ study.

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“Guidelines about the prevention of pregnancy-related VTE 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,” Middeldorp and Ankum wrote. “Epidemiological studies are a crucial step toward evidence-based guidance for tackling a frequent clinical question such as the need for prophylaxis of venous thromboembolism after induced abortion.” – by Andy Polhamus

Disclosures: The authors report no relevant financial disclosures. Middeldorp reports grants and personal fees paid to her institution from Aspen, Bayer and Daiichi Sankyo; as well as personal fees from BMS-Pfizer, Boehringer-Ingelheim, Portola and Sanofi. Ankum reports no relevant financial disclosures.