BACKGROUND Hypoxic complications are thought to be the result of vascular lesions in the maternal-placental or fetal-placental circulation, with a resultant decrease in blood flow. This study was designed 1) to explore what kind of pathophysiological changes occur in the maternal-placental-fetal circulations associated with acute fetal distress, and 2) to determine whether umbilical velocimetry can be used as a predictor of acute hypoxia in severe preeclampsia. METHODS Eighty-nine cases of severe preeclampsia, who had Doppler ultrasonography, maternal blood chemistry and hematogram examinations all performed within two days of delivery or fetal death, were studied. RESULTS According to the absence or presence of acute fetal distress as determined by the fetal heart rate pattern, patients were divided into two groups: distress group and non-distress group. There was no significant difference between the two groups in maternal general status. However, patients in the distress group had a significantly shorter gestation age on admission and at delivery (p < 0.00001). In the distress group, the perinatal outcome was poor. Newborns in the distress group had, significantly, a lower birthweight, and a higher incidence of SGA, 1-min Apgar scores of less than 7, and fetal acidosis (pH < 7.2) (p < 0.001). Doppler ultrasonography also showed a significantly higher incidence of abnormal umbilical artery Doppler waveforms in the distress group (p < 0.05). However, there was no difference between the two groups in the uterine artery Doppler velocimetry. Maternal blood chemistry and hematogram examinations revealed significantly higher blood levels of hemoglobin, hematocrit, blood urea nitrogen, and creatinine but lower levels of total protein and albumin in the distress group. An abnormal umbilical artery SD ratio (> 95th centile) as a predictor of acute fetal compromise, judged by the incidence of abnormal fetal heart tracing mandating emergency delivery, 1-minute Apgar scores of less than 7, 5-minute Apgar scores of less than 7, and a pH value for the umbilical arterial blood of less than 7.2, had a sensitivity of 40.5-75%, specificity of 71.8-80%, positive predictive value of 12.5-75%, and negative predictive value of 64.5-98.4%. CONCLUSIONS In severe preeclampsia, early onset of disease superimposed with maternal hemoconcentration might initiate an acute insult and predispose the fetus to acute hypoxia.