[Analysis of fetal reactions to acoustic stimuli with various registration technics].

The aim of the study was to standardize the types of fetal reactions to a short acoustical stimulation in relation to gestational age and the fetal behavioural state. We used polygraphic monitoring in 74 normal pregnancies to investigate the types of fetal reactions after an acoustical stimulation with a bell or a so-called larynx vibrator. A distinction was made between a very short reaction and a so-called long-term reaction with a long-lasting change in a fetal behavioural pattern. After the 26th gestational week, we observed at the so-called "passive" fetal stage a fetal reaction to the bell in 80% and a reaction to the vibrator in 100%. In the "active" fetal state, there was only a reaction in 54 and 62% of the fetuses respectively. The number of "long-lasting" reactions was relatively increased in the active state and after stimulation with the vibrator. After stimulation with the bell and the vibrator, the actocardiograph tracing showed a heart-rate acceleration in 76% and 61% respectively and a so-called cluster of fetal movements in 88% and 100% respectively. A fetal reaction to acoustical stimulation can be diagnosed most accurately by combining the heart-rate acceleration and the clustering of fetal movements. It still has to be checked to what extent a negative response to acoustical stimulation is indicative of possible fetal distress. In cases with negative tests, further monitoring methods have to be applied in order to exclude fetal hypoxia.