Predicting pH at Birth in Absent or Reversed End-Diastolic Velocity in the Umbilical Arteries

Abstract

To investigate arterial and venous blood flow in fetuses with absent or reversed end-diastolic flow in the umbilical arteries and to correlate the Doppler results with umbilical artery blood pH at birth to predict the probability of acidosis at birth. Ninety-one fetuses from singleton pregnancies without fetal malformations with a diagnosis of absent or reversed end-diastolic flow in the umbilical arteries were prospectively studied. On the day of delivery, Doppler velocimetry of the umbilical arteries, middle cerebral artery, and ductus venosus was performed and the results were correlated with umbilical artery pH at birth at the following cutoff levels: pH < 7.20, < 7.15, < 7.10, and < 7.05. The association between fetal arterial and venous Doppler velocimetry and acidosis was then individually analyzed by the chi(2) and Fisher exact tests. The ability of these tests to predict the probability of acidosis at birth was estimated using a logistic regression model. There was a negative correlation between pH at birth and umbilical artery pulsatility index (r = -0.39; P < .001) and pulsatility index for veins in the ductus venosus (r = -0.63; P < .001). Assessment of the fetal arterial circulation (middle cerebral artery) showed no statistical correlation with pH at birth. Using logistic regression analysis, probability curves were constructed for pH values less than 7.20 (odds ratio [OR] 8.03), less than 7.15 (OR 11.92), less than 7.10 (OR 12.16), and less than 7.05 (OR 8.20). The pulsatility index for veins of the ductus venosus was related to pH at birth, demonstrating that the higher the ductus venosus pulsatility index for veins, the lower the pH at birth. Once the pulsatility index for veins in the ductus venosus is known, the probability of acidosis at birth can be estimated.