Response of the premature fetus to stimulation by speech sounds.

The response of the premature fetus to speech stimuli was studied in 41 healthy pregnant patients at 26-34 weeks gestation. Speech stimuli consisted of repeated syllables ('ee' and 'ah') presented externally over the maternal abdomen at either 100, 105, or 110 decibels (dB). Sound stimuli were delivered during periods of both high and low fetal heart rate variability. During periods of low FHR variability, a decrease in fetal heart rate and an increase in the standard deviation of heart rate were found. During periods of high FHR variability, no significant change in either of these measures was observed. This is the first clear demonstration of heart rate responses to speech stimuli in the premature fetus. As is the case in the term fetus, this response is dependent on baseline heart rate variability which is the primary determinant of fetal state. The clinical usefulness of this finding may be limited by the magnitude of the response.