A comparison of the nonstress test, oxytocin challenge test, Doppler velocimetry and biophysical profile in predicting umbilical vein pH in growth-retarded fetuses.

Objective: To examine and compare the value of the nonstress test (NST), oxytocin challenge test (OCT), Doppler velocimetry (S/D ratio), and biophysical profile (BPP) in predicting fetal acidosis.

Method: NST, OCT, S/D ratio and BPP were performed in 23 pregnancies with growth-retarded fetuses. The value of each parameter in predicting fetal acidosis (umbilical vein pH obtained by cordocentesis) was examined.

Result: The NST, OCT and BPP were found to have the same positive predictive value of 57.1% in predicting fetal acidosis. The S/D ratio was found to have a very low positive predictive value (14.3%). The only combination of two parameters that showed improved positive predictive value, was that of OCT and NST (66.7%).

Conclusion: (1) The best indirect method in assessing fetal well-being is the combination of NST and OCT. (2) Since the positive predictive value of the indirect methods is still low, direct assessment of the fetal metabolic status is recommended in premature growth-retarded fetuses with an abnormal test.