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Doppler assessment of the fetal hemodynamics response to chronic hypoxia

The cardiovascular responses to fetal hypoxia are coordinated to centralize blood flow to the vital organs, such as the fetal brain. The most precise indicator of this redistribution, and fetal hypoxia, is the Doppler cerebral-umbilical ratio (C/U). Our goals were: 1. to study the cerebral and umbilical hemodynamics changes and to determine C/U ratio in growth-retarded and hypoxic fetuses, 2. to investigate if at long term, fetal brain hyperperfusion with loss of cerebrovascular reactivity is associated with brain damage and poor fetal outcome. Doppler flow velocity waveforms from the umbilical and middle cerebral arteries were recorded mainly every day during the second half of pregnancy in 7 growth-retarded and hypoxic fetuses. The C/U ratio was calculated as a parameter of fetal blood flow redistribution. The evolution of the fetal hemodynamics was interpreted according to the clinical, anatomical and histological data. All fetuses had poor fetal outcome including fetal death. Fetal blood flow redistribution in favor of fetal brain was detected in all cases during the whole period of observation. The development of oligohydramnios and the disappearance of the cerebral flow velocity variability characterized the early phase of fetal deterioration. During the later phase, fetal heart rate decelerations and the increase of cerebral vascular resistance with reduction of brain perfusion were detected. The histology of the fetal brains revealed hypoxic damages. The decrease in C/U ratio with the loss of cerebral flow velocity variability was associated in all fetuses with poor outcome. Our results also indicate that a loss of cerebrovascular reactivity occurred remarkably before changes in fetal heart rate.

fetal hypoxia; Doppler; brain damage

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