['Since the corpus luteum (CL) is known to play an important role in early pregnancy, its activity could possibly be a marker for pregnancy outcome.', 'The late estradiol (E2) concentration in 48 viable pregnancies and 39 pregnancies which resulted in spontaneous abortions after in vitro fertilization and embryo transfer were used to evaluate such predictability.', 'All patients studied were of the Center for Reproductive Medicine at Cornell University Medical College.', 'Eighty-seven patients.', 'None.', 'Serum E2 and human chorionic gonadotropin (hCG) concentrations on day +11, +13, +15 (day +1 = day of ovum pick-up) were measured and studied.', 'The late luteal CL activity after rescue had a positive correlation with the number and quality of the implanted embryos. Reduced CL activity was indicative of abortion. The late luteal E2 pattern when compared with hCG doubling time had a better abortion predictability (37.8% versus 63.9%, respectively).'] Are late luteal estradiol patterns a better prognosticator of pregnancy outcome than serial beta-human chorionic gonadotropin concentrations?