Developmental change in fetal response to repeated low-intensity sound.

The aim of this study was to investigate developmental changes in heart rate response to repeated low-intensity (85 dB) sound stimulation in fetuses between 32 and 37 weeks of gestation. We measured amplitude changes in heart rate as our index of fetal response. At 35 to 37 weeks of gestation, the majority of fetuses showed a deceleratory response at the first trial. Amplitude decreased with further trials using the same stimulus before recovering when exposed to another type of stimulation. In contrast, responses in fetuses at 32 to 34 weeks of gestation were variable across trials and there was no recovery with exposure to another type of stimulation. Our results suggest that fetal habituation of cardiac response changes with developmental age.