Middle cerebral artery Doppler indices at different sites: prediction of umbilical cord gases in prolonged pregnancies.

OBJECTIVES

To assess the value of middle cerebral artery Doppler indices obtained from different sampling sites in predicting umbilical cord gases at delivery in prolonged pregnancies.

METHODS

This was a prospective study of consecutive pregnant women referred for prolonged-pregnancy surveillance. The predictive value of distal and proximal middle cerebral artery Doppler indices for cord blood gases was evaluated in women who delivered within 48 h of their last antenatal test using stepwise multiple regression.

RESULTS

There was a significant linear correlation between proximal and distal middle cerebral artery pulsatility indices (R = 0.777; P < 0.0001), the mean values being 1.49 (SD, 0.45) and 1.56 (SD, 0.47), respectively. There was also a linear correlation between proximal and distal cerebroplacental ratios (R = 0.68; P < 0.0001), the mean values being 1.85 (SD, 1.96) and 1.92 (SD, 1.89), respectively. The stepwise multiple regression analysis for umbilical artery pH showed that once the distal middle cerebral artery pulsatility index was introduced into the model, the addition of any variable did not result in a significant improvement of the predictive capacity. The model showed a coefficient of determination (R(2)) of 0.079. There was a significant correlation between umbilical artery pO(2) and both proximal middle cerebral artery pulsatility index (positive) and the occurrence of elective Cesarean section (negative). This model accounted for 21% of the variance (R(2) = 0.21). No other variables added any significant prediction for pO(2).

CONCLUSIONS

In post-term pregnancies the proximal middle cerebral artery pulsatility index significantly predicts umbilical artery pO(2) at delivery but does not predict pH. There is a weak association between distal middle cerebral artery pulsatility index and pH but, as this only explains 8% of the variance, it is of little clinical value.