OBJECTIVE: to assess through Dopllerfluxometry the S/A ratio of the ductus venosus and determine the cut-off point to identify preterm fetuses with the 'brain sparing phenomenon". METHOD: a cross-sectional study was performed in 60 pregnant women that presented the "brain sparing phenomenon" (umbilical cerebral ratio >1) and gestational age between 25 and 33 weeks. The following parameters were studied: S/A ratio of the ductus venosus, pH and base excess (BE) of a fetal blood sample collected from the umbilical vein immediately after birth. The fetuses were classified according to the gas analysis result. They were considered abnormal when pH <7.20 and BE < -6 mmol/l. A receiver operator characteristic (ROC) curve analysis was performed to examine the relationship between S/A ratio and fetal acidemia. RESULTS: sixty pregnant women in the period of January 1998 to January 2003 were selected. In the moment of the study the gestational age varied from 25 to 33 weeks, with an average of 29.7 weeks (±1.8 weeks). All of the fetuses presented the "brain sparing phenomenon". Among them 14 presented abnormal gas analysis at birth and 46 presented normal gas analysis. The prevalence of fetuses with abnormal gas analysis in the studied material was 23.33%. Significant association was observed between the abnormal ductus venosus velocimetry and abnormal gas analysis at birth (chi2 = 784.44, p < 0.00001) in preterm fetuses with "brain sparing phenomenon". The best cut-off point of the S/A ratio (where the ROC curves bent) was 3.4. CONCLUSION: fetal acidemia in preterm fetuses with "brain sparing phenomenon" may be noninvasively identified by Doppler measurement of the ductus venosus when the S/A rises above 3.4.
Ultrasonography, Doppler; Blood gas analysis; Placental circulation; Dopplerfluxometry
