ObjectiveTo analyze whether first-trimester embryonic (fetal) heart rates (FHR) are useful in predicting pregnancy outcome for infertility patients.MethodsPatients in a university-based reproductive endocrinology and infertility practice were studied prospectively. Infertile women who achieved clinical pregnancy underwent first-trimester transvaginal sonographic evaluation, and FHR in patients achieving viable pregnancies were compared with those experiencing fetal loss.ResultsOverall, 99 pregnancies reached viability and 17 resulted in fetal loss before 20 weeks' gestation. Patient age, methods of conception, and number of previous fetal losses did not differ significantly between the two groups. A significant correlation (r= .70,P< .00l) was found between increasing FHR levels and advancing gestational age in patients with viable pregnancies and, although to a weaker extent, patients who miscarried (r= .52,P< .05). A significantly higher number of viable pregnancies, compared with fetal losses, had FHR falling within one (70.7% compared with 41.2%,P< .025) and two (99.0% compared with 64.7%,P< .00l) standard deviations of the mean for viable pregnancies at corresponding gestational ages. The majority of FHR of failing pregnancies fell below the individual reference ranges.ConclusionFirst-trimester FHR can help predict pregnancy outcome for infertility patients. Women with FHR outside the reference range from the mean for viable preg-nancies at corresponding gestational ages may be at risk for eventual pregnancy loss.