Central and peripheral hemodynamic changes in fetuses with absent end-diastolic velocity in umbilical artery: correlation with computerized fetal heart rate pattern.

OBJECTIVES

Our purpose was to study hemodynamic changes in peripheral and central blood vessels and to correlate these changes with the computerized fetal heart rate pattern in fetuses with absent end-diastolic velocity in the umbilical artery.

STUDY DESIGN

Doppler studies of the umbilical artery, the middle cerebral artery, and aortic and pulmonic outflow, together with computerized fetal heart rate monitoring, were performed every 2 to 4 days until delivery in 13 fetuses with absent end-diastolic velocity in the umbilical artery. The pulsatility index was calculated from the flow velocity waveforms obtained from the umbilical and middle cerebral arteries. The velocity time integral (an index of cardiac output) and the heart rate were calculated from the flow velocity waveforms obtained from the aortic and pulmonic outflow.

RESULTS

Two fetuses were delivered immediately after the first examination because of repetitive fetal heart rate decelerations. One fetus was excluded from the study because of major malformations. Ten had three to eight tests each. Six had a biphasic change of the middle cerebral artery, which consisted of a decrease (p < 0.001) followed by an increase in the pulsatility index (p < 0.05). When the middle cerebral artery lost its vasodilation, there was an increase in the middle cerebral artery/umbilical artery pulsatility index ratio (p < 0.05). Left cardiac output decreased (p < 0.05), resulting in an increase in the pulmonary/aortic velocity time integral x heart rate ratio (p < 0.05). Reduced fetal heart rate variation (< 30 msec) developed in all six fetuses, and they were delivered because of repetitive fetal heart rate decelerations. Four fetuses with only a decrease in the middle cerebral artery pulsatility index did not have reduced fetal heart rate variation or decelerations, the aortic velocity time integral x heart rate didn't decrease, and the pulmonic/aortic velocity time integral x heart rate ratio didn't increase. These fetuses were delivered for reasons other than fetal distress. The middle cerebral artery pulsatility index correlated with the aortic velocity time integral x heart rate (r = -0.53, p < 0.0001), and the middle cerebral artery/umbilical artery pulsatility index correlated with the pulmonic/aortic velocity time integral x heart rate (r = 0.56, p < 0.0001).

CONCLUSION

Abnormal fetal heart rate patterns occur in fetuses with absent end-diastolic velocity in the umbilical artery when the middle cerebral artery begins to lose its compensatory maximal dilation. The increase in the middle cerebral artery pulsatility index is associated with a significant reduction in left ventricular output without significant changes in right ventricular function. Thus it appears that a loss of autonomic reactivity occurs in the brain first and is followed within a few days by a similar response in the heart, as shown by the decreased fetal heart rate variation.