CHANGES IN UMBILICAL ARTERIAL AND VENOUS-BLOOD FLOW VELOCITY WAVE-FORMS DURING LATE DECELERATIONS OF THE FETAL HEART-RATE

Objective: To compare umbilical arterial and venous Doppler velocity w aveforms during labor in fetuses with normal heart rate tracings and f etuses with late decelerations. Methods: During labor, umbilical arter ial and venous Doppler flow velocity waveforms were obtained between a nd during contractions in 20 fetuses (ten with normal heart rate traci ngs and ten with late declerations). The umbilical arterial systolic-d iastolic (SID) velocity ratios were compared, and umbilical venous vel ocities were examined for the presence or absence of venous pulsations . Results: Fetuses with late decelerations had a significant increase in the umbilical arterial S/D ratio between contractions compared to n ormal fetuses (2.43 +/- 0.74 versus 1.56 +/- 0.27, P = .003). There wa s no significant difference in S/D ratios obtained between contraction s compared with those obtained during contractions in either the norma l or late deceleration group. Umbilical venous pulsations were signifi cantly more common (90 versus 0%, P < .00001) during contractions in f etuses with late decelerations; umbilical venous pulsations were not s een in these fetuses between contractions and were not present at any time in fetuses with normal heart rate tracings. Conclusions: Increase d umbilical arterial velocity ratios and the presence of umbilical ven ous pulsations during contractions in fetuses with late decelerations suggest that the cardiovascular pathophysiology of late decelerations involves changes in placental resistance as well as cardiac performanc e. The presence of umbilical venous pulsations during late deceleratio ns is consistent with the hypoxic fetal cardiovascular changes (hypert ension and myocardial depression) previously reported from animal stud ies.