Behavioural state change in normal human fetuses following a single vibroacoustic stimulus: effect of duration of quiet sleep prior to stimulation.

We examined 96 normal human fetuses between 37 and 41 weeks of gestation to determine the relationship between the duration of the active state following a single vibroacoustic stimulus (VAS) and the time spent in prestimulus state 1F, i.e. quiet sleep (QS). All fetuses were observed to enter state 1F prior to testing. After remaining in this state for 3 min, each fetus was randomized into one of three groups: no stimulation (Group I, N = 32); a single 1-s VAS delivered after 3-5 min of QS (Group II, N = 33); and a single 1-s VAS delivered after 18-20 min of QS (Group III, N = 31). Fetuses in Groups I, II, and III were otherwise behaviourally indistinguishable. Heart rate and eye and body movements were monitored until the fetus either returned to state 1F and remained in that state for 3 min or did not return to state 1F within 60 min. Of the 64 fetuses who were stimulated, 62 responded, indicating that there was no effect of prestimulus state duration on the sensitivity to VAS. Fetuses stimulated after 18-20 min of QS behaved similarly to fetuses who entered an active period spontaneously.(ABSTRACT TRUNCATED AT 250 WORDS)