Objective: To determine the diagnostic performance of NST, AFI and modified-BPP for screening fetal acidemia in high-risk pregnancies.
Design: Diagnostic tests.
Setting: Srinagarind (tertiary) Hospital, Faculty of Medicine, Khon Kaen University.
Material and Method: Between April 2000 and August 2001, we included 185 high risk singleton pregnancies, GA> 37 weeks, with NST and AFI once a week until delivery. Immediately after delivery, the umbilical artery blood gases were evaluated. Fetal acidemia was defined as an umbilical artery pH < 7.15. An abnormal modified-BPP was identified when either the NST was non-reactive or the AFI was < 5 cm.
Results: Thirteen high risk pregnancies were excluded because the last test was more than 7 days before delivery. Of the remaining 172 pregnancies, total fetal acidemia was identified in 19 cases. The incidence of fetal acidemia was 11.05% (95% CI 6.63-15.73). Among the 19 cases, eight had non-reactive NST, and 11 had AFI < 5 cm but 14 with abnormal modified-BPP. The sensitivity of NST, AFI and modified-BPP was 42.11% (95% CI 34.73-49.48), 57.89% (95% CI 50.52-65.27), and 73.68%. (95% CI 67.10-80.27), respectively. The specificity, PPV, NPV, accuracy of NST, AFI and modified-BPP were high but not statistically different.
Conclusion: The modified-BPP had a significantly higher sensitivity than NST or AFI alone in screening for fetal acidemia, so a modified-BPP should be used to screen for fetal acidemia in high-risk pregnancies.

Keywords: Modified biophysical profile, Non-stress test, Amniotic fluid index, Fetal academia