Liu N, et al. - Researchers examined women whose first pregnancy ended with induced abortion, to evaluate their proneness to develop venous thromboembolism. Compared with a matched non-pregnant woman, the 42-day risk of venous thromboembolism after an induced abortion was double. Also, after an induced abortion vs after a livebirth, this risk was observed to be significantly lower. To rule out venous thromboembolism after induced abortion, a lower threshold for ordering a diagnostic test could be considered by clinicians compared to they would in a non-pregnant woman.

Methods

• Researchers used data from the universal health-care system of Ontario, Canada, to perform this propensity score-matched cohort study including primigravid women who had an induced abortion between Jan 1, 2003, and Dec 31, 2015.
• Using propensity score, these women were matched to primigravid women who had a livebirth (1:1) or nulligravid women who were not pregnant on the procedure date of their matched counterpart and who did not conceive within 1 year afterwards (5:1).
• Women younger than 15 years or older than 49 years and individuals who had missing or invalid information about their sex, area of residence, residential income, or world region of origin, were excluded.
• Risk of any venous thromboembolism within 42 days of the index date (defined as the date of an induced abortion, delivery date for livebirth, or for non-pregnant women the induced abortion date of their matched counterpart) was the primary outcome.
• The rate of venous thromboembolism in primigravid women who had an induced abortion was compared with the rate of venous thromboembolism in propensity-score-matched non-pregnant women and propensity-score-matched primigravid women whose pregnancy ended with a livebirth.
• They used Cox proportional hazard models to generate hazard ratios (HRs) of 42-day risk of venous thromboembolism after induced abortion.

Results

• A total of 194,086 eligible women whose first pregnancy ended with induced abortion were identified.
• Of these women, 176,001 (90·7%) could be matched with women whose first pregnancy ended in delivery of a newborn and also with 880,005 non-pregnant women.
• Findings revealed 30·1 (95% CI 22·0–38·2) per 100,000 women vs 13·5 (11·1–16·0) per 100,000 women was the estimated rate of venous thromboembolism within 42 days of an induced abortion vs in the non-pregnant group (HR 2·23, 95% CI 1·61–3·08).
• They found the HR was 0·16 (95% CI 0·12–0·22) when compared with the women in the livebirth cohort, whose venous thromboembolism rate within 42 days postpartum was 184·7 (95% CI 164·6–204·7) per 100,000 women.