Short-term adverse outcomes after mifepristone-misoprostol versus procedural induced abortion: a population-based propensity-weighted study

Background — Prior studies comparing first-trimester pharmaceutical induced abortion (IA) with procedural IA were prone to selection bias, were underpowered to assess serious adverse events (SAEs), and did not account for confounding by indication. Starting in 2017, mifepristone–misoprostol was dispensed at no cost in outpatient pharmacies across Ontario, Canada.

Objective — To compare short-term risk for adverse outcomes after early IA by mifepristone–misoprostol versus by procedural IA.

Design — Population-based cohort study.

Setting — Ontario, Canada.

Patients — All women who had first-trimester IA.

Measurements — A total of 39 856 women dispensed mifepristone–misoprostol as outpatients were compared with 65 176 women undergoing procedural IA at 14 weeks’ gestation or earlier within nonhospital outpatient clinics (comparison 1). A total of 39 856 women prescribed mifepristone–misoprostol were compared with 8861 women undergoing ambulatory hospital-based procedural IA at an estimated 9 weeks’ gestation or less (comparison 2). The primary composite outcome was any SAE within 42 days after IA, including severe maternal morbidity, end-organ damage, intensive care unit admission, or death. A coprimary broader outcome comprised any SAE, hemorrhage, retained products of conception, infection, or transfusion. Stabilized inverse probability of treatment weighting accounted for confounding between exposure groups.

Results — Mean age at IA was about 29 years (SD, 7); 33% were primigravidae. Six percent resided in rural areas, and 25% resided in low-income neighborhoods. In comparison 1, SAEs occurred among 133 women after mifepristone–misoprostol IA (3.3 per 1000) versus 114 after procedural IA (1.8 per 1000) (relative risk [RR], 1.87 [95% CI, 1.44 to 2.43]; absolute risk difference [ARD], 1.5 per 1000 [CI, 0.9 to 2.2]). The respective rates of any adverse event were 28.9 versus 12.4 per 1000 (RR, 2.33 [CI, 2.11 to 2.57]; ARD, 16.5 per 1000 [CI, 14.5 to 18.4]). In comparison 2, SAEs occurred among 133 (3.4 per 1000) and 27 (3.3 per 1000) women, respectively (RR, 1.04 [CI, 0.61 to 1.78]). The respective rates of any adverse event were 31.2 versus 24.9 per 1000 (RR, 1.25 [CI, 1.04 to 1.51]).

Limitation — A woman prescribed mifepristone–misoprostol may not have taken the medication, and the exact gestational age at IA was not always known.

Conclusion — Although rare, short-term adverse events are more likely after mifepristone–misoprostol IA than procedural IA, especially for less serious adverse outcomes.