The relationship between fetal biophysical assessment, umbilical artery velocimetry, and fetal acidosis.

In a prospective study of 62 patients undergoing cesarean delivery before the onset of labor, fetal biophysical assessment and umbilical artery systolic-diastolic ratios (S/Ds) were performed within 3 hours of delivery. There was a significant relationship between the fetal biophysical profile score and cord arterial as well as cord venous pH. However, there was no identifiable relationship between S/D and cord arterial or venous pH. The efficacies of the biophysical components alone (nonstress test [NST] and fetal biophysical profile) and in combination with S/D to predict fetal acidosis were determined. The NST had the best sensitivity (100%) and negative predictive value (100%). The fetal biophysical profile had the best specificity (91%), positive predictive value (62%), and overall efficiency (90%). The S/D had the lowest sensitivity (66%), specificity (42%), positive predictive value (16%), negative predictive value (88%), and overall efficiency (45%). The addition of S/D to the NST or fetal biophysical profile did not improve diagnostic accuracy. These data suggest that the NST should be used as a primary test for the antepartum detection of fetal acidosis, whereas the fetal biophysical profile is a reasonable adjunct test. The umbilical artery S/D, as determined by continuous-wave Doppler velocimetry, has no value as a primary method or an adjunct in the antepartum detection of fetal acidosis.