In the present study, we intended to depict the changes occurring during labor in the fetal umbilical blood flow. Simultaneously, we also investigated the characteristics of the changes and their relation to the fetal heart rate patterns. In 15 human labors, the blood flow velocity in the intra-abdominal part of the umbilical vein was recorded continuously by the pulsed Doppler ultrasound technique. At the same time, direct fetal ECG and uterine contraction were monitored. The umbilical venous blood flow during the uterine contraction was equal to or lower than that between the uterine contractions. The maximum umbilical blood flow was decreased by 50% or more at variable deceleration and reduction of the umbilical venous blood flow was followed by a decrease in heart rate. Otherwise at late deceleration, the umbilical venous blood flow reduction was not so marked and biphasic pulsation became evident following the heart rate decrease. The present study has revealed that the umbilical venous blood flow shows characteristic patterns at variable deceleration and late deceleration.