The predictive value of fetal acoustic stimulation

To compare the predictive abilities, test duration times, and incidence of nonreactive results in the acoustic stimulation test (AST) and the nonstress test (NST).

Four-hundred randomly selected patients, delivering within 7 days of a preceding test, were divided into two groups (group I: NST; group II: AST). In the AST group, fetal heart rate tracing were recorded for the first 5 minutes as a baseline recording. If the reactivity criterion was not met, transabdominal acoustic stimulation to the fetal head was performed. In the NST group, nonreactive tests were followed by a repeat NST. In both groups, nonreactive tests were followed by oxytocin challenge test (OCT) on the same day. Depressed 5-minute Apgar scores (< 7) and an umbilical arterial blood pH of < 7.2 were taken as indicators of fetal distress. Sensitivity, specificity, and predictive values of NST and AST were calculated and compared.

The incidence of nonreactive tests was lower in the AST group. AST decreased the test duration time by 10.1 minutes. The sensitivity values were 87.5% in the NST group and 85.7 in the AST group; specificities of were found to be 94% for AST and 88% for NST. The negative predictive value was found to be 98% in each group, but the positive predictive value was 54.5% in the AST group and 38.8% in the NST group.

AST offers benefits, by decreasing the incidence of nonreactive tests and reducing the test time. AST lowers the rate of false positives without changing the negative reliability of NST. It is a safe test and allows more efficient use of perinatal services.