In this preliminary investigation, we sought evidence of increasing impedance to placental blood flow from both sides of the placenta and evidence of compromised fetal aortic blood flow in 35 human pregnancies exceeding 42 weeks' gestation. Fetal age was confirmed by biparietal diameter (BPD) measurements obtained before 21 weeks. Pourcelot's Index, calculated from Doppler sonograms recorded with a noninvasive technique from small arteries in the myometrium and from an umbilical cord artery, did not correlate with the duration of the pregnancy beyond term. However, this “resistance index” of Pourcelot was higher in the umbilical cord arteries of fetuses with a worse clinical outcome. Doppler blood cell velocity in the fetal descending aorta correlated significantly and negatively with the prolongation of gestation. Fetal aortic velocities appeared to be lower in fetuses who passed meconium before delivery. Our findings suggest that fetal compromise in prolonged pregnancy is more a fetal-placental problem than a uteroplacental problem.