The relationship between the umbilical artery systolic/diastolic ratio and umbilical blood gas measurements in specimens obtained by cordocentesis.

The purpose of this investigation was to prospectively determine the relationship between the umbilical artery systolic/diastolic ratio and the umbilical blood gases in samples obtained from 165 fetuses during diagnostic cordocenteses. In each instance the sample was the umbilical vein. The systolic/diastolic ratio was measured in a midsection of the umbilical cord. Analyses used stepwise, multiple linear regression. The mean +/- SEM gestation was 29 +/- 0.4 weeks; 72% of fetuses were greater than or equal to 25 weeks and were considered potentially viable. There was no relationship between the umbilical artery systolic/diastolic ratio and pH, PCO2, or PO2 in fetuses either less than 25 weeks' gestation or greater than or equal to 25 weeks' gestation but with systolic/diastolic ratios greater than or equal to the 95th percentile for control fetuses at 25 weeks' gestation with normal blood gas values (3.5). In fetuses greater than or equal to 25 weeks' gestation with systolic/diastolic ratios that exceeded 3.5 (n = 37), there was a strong relationship between the systolic/diastolic ratio and the umbilical venous PO2 (r = -0.68, p less than 0.0001), which was independent of gestational age. Each fetus with repetitively absent-reversed umbilical artery diastolic blood flow and a heart rate greater than 90 beats/min (n = 6) had blood gas measurements consistent with hypoxia and acidosis. This investigation suggests that factors that lead to an increase in the umbilical artery systolic/diastolic ratio are associated with a progressive impairment of placental gas exchange and that by the time diastolic flow is lost, hypoxemia is present.