The nonstress test (NST) has been known to be a reliable means of testing for antepartum fetal well-being, especially in high-risk pregnancy. But the problem with NST is that often the fetus is quiescent or asleep at the time of testing. Moreover frequently considerable time is spent waiting for sufficient activity to correctly inter-pret results.
In order to improve the efficacy of testing the author prospectively evaluated the adjunctive use of acoustic stimulation test (AST) from June 1985 to March 1986. The authors present our observations of auditory response to the fetus with the use of Sound Generator (Pulse range; 350~3,300 Hertz, Sound pressure level range; 100"-125 decibel). A five second stimulation of 1,220 cycle/second pure-tone sound was used at 110, 115 and 120. decibel. The method was applied to 56 normal and 119 high-risk pregnant women.
In normal pregnancy, the incidence of reactive test, of AST(98.2%) was higher than that of NST´ (87.5%) (p =´.028). In high-risk pregnancy, especially in the patients with pregnancy induced hypertension, the incidence -of reactive test -of AST (100%) was higher than, that of NST (78.9%) (p=.034).
Among the normal pregnancy, the frequency of nonreactive tests in the NST and AST were 12.5% and 1.8%, respectively. Among the high risk pregnancy, the fre-quency of nonreactive tests in the NST and AST were 11.8% and 5.9%, respectively. Thus the AST reduces the frequency of the nonreactive tests in both groups, the ratio of the frequency of AST to NST being 1/7 in normal pregnancy and 1/2 in high risk pregnancy.
A significant reduction of testing time (1/3) was also observed in AST as compared with.NST. This simple and safe AST offers advantage over the traditional NST by increasing the reactivity, decreasing the nonreactivity and reducing testing time.
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