Objective: To determine which antepartum test is the best predictor of post-date-related adverse outcome among the amniotic fluid index (AFI), nonstress test (NST), biophysical profile, or middle cerebral artery to umbilical artery Doppler ratio.
Methods: Pregnant women of 41 or more weeks' gestation with singleton fetuses and vertex presentations underwent antepartum testing twice a week. Pulsed Doppler ultrasound was used to obtain the flow velocity waveforms from the umbilical and middle cerebral arteries. Adverse post-date-related outcome was defined as the occurrence of meconium aspiration syndrome, cesarean delivery for fetal distress, or fetal acidosis. The predictive values of an AFI equal to or less than 5 cm, a biophysical profile score equal to or greater than 6, a nonreactive NST, and a middle cerebral artery to umbilical artery ratio less than 1.05 in identifying adverse outcome were compared.
Results: Forty-nine women met the inclusion criteria; ten (20.4%) had an adverse outcome. A middle cerebral artery to umbilical artery ratio of less than 1.05 was found to be the best predictor of adverse outcome, with a sensitivity of 80%, specificity of 95%, positive predictive value of 80%, and negative predictive value of 95%. The other three diagnostic tests had sensitivities equal to or less than 40%. The middle cerebral artery to umbilical artery ratio was also a better discriminator of adverse outcome than either the umbilical artery systolic-diastolic (S/D) ratio or the middle cerebral artery S/D ratio.
Conclusion: Although the sample size of our study was small, the results suggest that a middle cerebral artery to umbilical artery ratio of less than 1.05 is an accurate method of predicting post-date-related adverse outcome.