Umbilical artery Doppler flow-velocity waveforms and fetal acid-base balance in Rhesus-isoimmunized pregnancies

Pulsed Doppler blood-flow velocity waveforms in the umbilical arteries, as well as blood gases, hematocrit, and lactate concentration in umbilical venous blood, were examined in 21 patients undergoing 49 cordocentesis, 34 of which were followed by fetal blood transfusion into the umbilical vein. The aim of the study was to evaluate the correlations, if any, between the Doppler indices from the umbilical artery (pulsatility index, resistance index, systolic/diastolic ratio) and the blood gas values (pO2, pCO2, O2 content, pH) and lactate content in the umbilical vein. The only correlation confirmed in this study was in the subgroup of anemic fetuses undergoing fetal blood transfusion, where correlation existed between A/B and the initial O2 content (r = -0.41, p < 0.02). We conclude that, in Rhesus-isoimmunized pregnancies, in contrast to other pregnancies, a close correlation does not exist between the Doppler indices in the umbilical artery and the fetal blood gas values.