Eighty-two patients at 287 days' gestation or longer were tested by nonstress test (NST), amnioscopy, ultrasound assessment of amniotic fluid volume, and Doppler velocimetry. Several maternal and fetal arteries were analyzed: uterine, umbilical, descending thoracic aorta, renal, and middle cerebral. During the study, other maternal-fetal functional indices were recorded: hPL, estriol, hematocrit, platelets, mean platelet volume, and uric acid. No abnormalities were found in the uterine, umbilical, middle cerebral, thoracic descending aorta, and renal artery velocimetry in post-dates gestations. However, a significant reduction of the time-averaged mean velocity in the descending thoracic aorta was associated with an increased incidence of oligohydramnios, meconium-stained fluid, abnormal NST, and cesarean delivery for fetal distress. The present study suggests that serial Doppler flow measurements of mean velocity of the fetal descending thoracic aorta may be a simple and rapid technique for identifying prolonged pregnancies at increased risk for perinatal complications.