Objective: Early documentation of fetal cardiac activity in patients undergoing in vitro fertilization/embryo transfer (IVF/ET) predicts successful outcome in approximately 85% of cases. However, the importance of maternal age as predictor of pregnancy outcome after early detection of cardiac activity is unclear.Design: A retrospective review of220 pregnancies in 202 women undergoing IVF/ET.Materials and Methods: Records of patients undergoing treatment for infertility in a University setting between 1993 and 1996 were considered. The range of ages in the study population was 23 to 42 years. Patients were further classified by diagnosis according to the etiology of their infertility. Clinical pregnancies were defined as the presence of cardiac activity by transvaginal ultrasound 35 to 42 days after embryo transfer. Live births refer to pregnancies resulting in delivery of a viable infant. Each multiple gestation in which any cardiac activity was observed is recorded as one pregnancy, regardless of the number of live births.Results: Fetal loss occurred in 2 of 66 pregnancies after detection of fetal cardiac activity in the group less than 30 years of age. A spontaneous loss rate of 5.7% was observed for maternal ages between 31 and 35 years versus 16% for women aged 36 to 39 years (OR = 9.2%; 95% CI = 3.3 to 28; P < 0.05). A five-fold increase in pregnancy loss was observed for women greater than or equal to 40 years of age when compared to women between 31 and 35 years old (5.7% versus 29% P < 0.005). The etiology of infertility did not influence outcome.Conclusions: Infertile women have an increased susceptibility to pregnancy loss, which may be age dependent. After detecting cardiac motion, the incidence of pregnancy loss is increased by age. Women over 40 years old should be informed that their risk of pregnancy loss (29%) is approximately five times greater than that of women 31 to 35 years of age.