RESUMEN
OBJECTIVES: The main aim of the study was to establish a threshold for serum human chorionic gonadotropin (hCG) level that ruled out ongoing pregnancy after induced medical abortion (MA). The secondary aim was to discover risk factors for the need for uterine aspiration. METHODS: This prospective study included women who underwent MA with mifepristone-misoprostol at ≤9 weeks of gestation between 2012 and 2014. Serum hCG levels were measured 14-21 days after MA. The main outcome measure, ongoing pregnancy, was defined as the presence of an embryo with cardiac activity on transvaginal ultrasonography after MA. The receiver operating characteristic curve was plotted to determine the optimal serum hCG threshold. Risk factors for the need for uterine aspiration were calculated using multivariate logistic regression and expressed as odds ratios (ORs) with 95% confidence intervals (CIs). RESULTS: The study included 814 women. Mean gestational age was 46.5 ± 7.4 days for ongoing pregnancies and 44.2 ± 4.8 days for MA success (p = .43). The ongoing pregnancy rate after MA was 0.9%. A serum hCG threshold ≥900 IU/l to diagnose ongoing pregnancy gave 100% sensitivity and 81.5% specificity, compared with 85.7% sensitivity and 83.5% specificity using a threshold ≥1000 IU/l. Independent risk factors for uterine aspiration requirement were: gravidity (OR 3.8; 95% CI 1.1, 13.2; p = .001), gestational age >6 weeks (OR 6.0; 95% CI 1.8, 6.0; p = .006) and previous surgical abortion (OR 2.4; 95% CI 1.1, 5.2; p < .001). CONCLUSION: Serum hCG measurement <900 IU/l, 14-21 days after MA, is an efficient strategy for excluding ongoing pregnancy after first trimester MA.