['To determine the predictive value(s) of beta-hCG serum levels for pregnancy outcome following blastocyst transfer.', 'Retrospective review.', 'University-based assisted reproductive technology (ART) program.', 'All ART patients enrolled from January 1998 to December 1999.', 'None.', 'Beta-hCG serum levels and pregnancy outcomes.', 'Of the 836 ART cycles initiated, 608 embryo transfers met study criteria and were assigned to one of two groups: 248 day 5 blastocyst transfers or 360 day 3 embryo transfers. In the day 5 blastocyst group, 147 pregnancies occurred (59.2%), and day 3 transfers resulted in 165 pregnancies (45.8%). For day 3 and day 5 transfers, mean values of beta-hCG on day 16 post-retrieval of spontaneous abortions were lower than ongoing pregnancies (P< .05). A beta-hCG value on day 16 of >300 mIU/mL predicted an ongoing pregnancy for day 5 transfer group in 97% of pregnancies compared with 92% for day 3 embryo transfers. A multiple gestation was observed in 70% of pregnancies with a beta-hCG level >400 mIU/mL in the day 5 group compared with 63% for the day 3 group. The incidence of higher-order multiple gestations was significantly lower in the day 5 blastocyst group (P< .05).'] Are human chorionic gonadotropin levels after blastocyst transfer highly predictive of pregnancy outcome?