The fetal acoustic stimulation test: a reliable and cost effective method of antepartum fetal monitoring.

RATIONALE A healthy foetus, if exposed to external sound stimulation, often responds with vigorous movements which can be felt by the mother. A hypoxic foetus usually does not show this response. OBJECTIVES To evaluate the fetal acoustic stimulation test (FAST) in antepartum fetal monitoring. DESIGN AND SETTING Prospective interventional study carried out at the Teaching Hospital, Galle. METHOD An initial non-stress test (NST) followed by a FAST using the Corometric model 146 was carried out in 423 high risk pregnant women. The response to FAST was assessed and compared with the NST. A repeat NST was recorded in women who had an initial non-reactive NST. The results of the NST and FAST were compared with the fetal outcome if the woman delivered within 24 hours. OUTCOME MEASURES Maternal perception of fetal movements after FAST, results of NST before and after FAST, and the babies' 5 minute Apgar scores if delivered within 24 hours of the FAST. RESULTS Of the women, 349 (82.5%) noticed fetal movements after FAST. Of the 167 women who complained of absent or reduced fetal movements, 67% felt fetal movements after FAST. Ninety one had a nonreactive NST and 43 (47%) became reactive after FAST. Compared to the NST, the FAST had less sensitivity (93% vs 100%, p = 0.01), better specificity (79% vs 45%, p = 0.001), better positive predictive value (67% vs 50%, p = 0.02), similar negative predictive values (96% vs 100%, p > 0.05) and better accuracy (83% vs 69%, p = 0.03) in predicting neonatal asphyxia (5 minute Apgar score < 7) if the baby was delivered within 24 hours after the test. CONCLUSION The FAST is a reliable, cost effective screening test for antepartum fetal monitoring. It significantly reduces the false positive (non-reactive) NST and has a good negative predictive value.