Fetal habituation to repeated sound stimulation.

Habituation is the progressive decrement of response with repeated stimulation. Neonatologists use this phenomenon to assess newborns for various pathological conditions of the CNS. The present study examined the time required for habituation of the startle response in 103 fetuses at various gestational ages (32 to 40 weeks). The external stimulus was produced by a door buzzer (80 to 90 db). Habituation time decreased as gestational age increased. About 85% of the fetuses showed habituation after less than 20 stimuli, and about 95% after less than 30 stimuli. In all cases habituation time never exceeded 50 stimuli.