Likelihood of live birth with extremely low β-hCG level 14 days after fresh embryo transfer

Objective To investigate the pregnancy outcomes of patients with low serum β-hCG level 14 days after day 3 embryo transfer.Methods A retrospective study was performed with 723 patients with a serum β-hCG level between 5 and 100 mIU/ml 14 days after embryo transfer. Pregnancy outcomes (live birth, clinical pregnancy) were analyzed according to the female patients’ age. ROC curves were plotted to indicate the threshold for prediction of clinical pregnancy and live birth.Results Of the 723 patients with serum β-hCG level <100 mIU/mL, 85.6% (619) had biochemical pregnancy, and only 14.4% (104) had clinical pregnancy (including 4.3% with live birth, 3.7% with ectopic pregnancy, and 6.1% with early miscarriage). The rate of live birth was significantly lower in ≥38-year group ,compared with <38-year group (1.3% vs. 5.1%, p = 0.045). The rates of biochemical pregnancy in patients with serum β-hCG of 5–25 mIU/mL and 26–50 mIU/mL were 99.5% and 92.4%, respectively. The serum β-hCG level to predict clinical pregnancy was 44.8 mIU/ml (sensitivity, 90.4%; specificity, 82.1%). For live birth, the serum β-hCG level was 53.7 mIU/ml (sensitivity, 90.3%; specificity, 81.1%).Conclusions The likelihood of live birth was minimal with low serum β-hCG level 14 days after embryo transfer.