Uterine Artery Doppler velocimetry is widely applied to predict pregnancy outcomes. Recent studies of uterine artery early diastolic notch demonstrate that it is good marker for fetal well-being. The early diastolic notch represents the reflected wave of uteroplacental circulation. The degree of back flow is reflected by the depth of the notch. The authors propose a new Doppler parameter, notch index(early diastolic velocity/maximum diastolic velocity) which is a better indicator of adverse perinatal outcomes than the isolated finding of an early diastolic notch. Its ability to predict adverse perinatal outcomes was evaluated in 121 pregnant women beyond the 28th weeks of gestation showing early diastolic notch. The incidence of adverse perinatal outcome(five minute Apgar score<7, cesarean section due to fetal distress, admission to neonatal intensive care unit, or perinatal death) was 100 % when the notch index was below 0.7. When the notch index range was 0.7~0.8, 0.8~0.9 and greater than 0.9, the incidence of adverse perinatal outcome was 72.4%, 46.6%, and 25 %, respectively. This study suggests that notch index could be used as new a marker to predict adverse perinatal outcome.