Changes in umbilical arterial and venous blood flow velocity waveforms during late decelerations of the fetal heart rate

Objective: To compare umbilical arterial and venous Doppler velocity waveforms during labor in fetuses with normal heart rate tracings and fetuses with late decelerations. Methods: During labor, umbilical arterial and venous Doppler flow velocity waveforms were obtained between and during contractions in 20 fetuses (ten with normal heart rate tracings and ten with late decelerations). The umbilical arterial systolic-diastolic (S/D) velocity ratios were compared, and umbilical venous velocities were examined for the presence or absence of venous pulsations. Results: Fetuses with late decelerations had a significant increase in the umbilical arterial SM ratio between contractions compared to normal fetuses (2.43±0.74 versus 1.56±0.27, P=.003)