Eighty-three healthy pregnant women between 26 and 40 weeks' gestational age were studied to examine effects of a 5-second external vibratory acoustic stimulus on the fetal heart rate, fetal breathing, and gross fetal body movement patterns. There was an immediate fetal heart rate response, following stimulus, characterized by an increase in duration of fetal heart rate accelerations from 26 ... [Show full abstract] weeks to term with an increase in basal fetal heart rate after 30 weeks. There was also a delayed response after 33 weeks' gestation, which consisted of an increase in the number of fetal heart rate accelerations and the incidence of gross fetal body movements for up to 1 hour after a 5-second stimulus with the electronic artificial larynx. Term (36 to 40 weeks) fetuses made breathing movements more irregularly after vibratory acoustic stimulation. We suggest that human fetal responses to stimulation with the electronic artificial larynx may reflect a functional maturation of the fetal central nervous system.