Fetal behavioural states and controlled sound stimulation

The aim of this study was to investigate responses of human fetuses near term (37-42 wks) (increase/decrease of fetal heart rate and/or fetal motility) to acoustic stimuli. The study group consisted of 43 patients and the control group of 27 patients. Polygraphic recordings of 5 different fetal variables were carried out synchronously for the categorization of the actual fetal behavioural state according to Nijhuis et al. (Nijhuis, J.G., Prechtl, H.F.R., Martin, C.B., Jr. and Bots, R.S.A.M. (1982): Early Hum. Dev., 6, 177-195). Controlled acoustic stimulation was performed either with sine wave tone (2 kHz, 120 dB and 5 s duration) or modulated sine wave tone (0.5-2 kHz, 'sawtooth' modulation, 120 dB and 5 s duration). An additional group of patients received 'sham' stimulation. Overall 84 acoustic stimulations have been carried out. In 26 out of 84 stimulations (30%) a fetal response could be observed within 5 s after acoustic stimulation. In general, there were far fewer fetal responses in sleep states than in states of wakefulness. Whereas in state 1 F only 1 out of 28 acoustic stimulations was followed by an immediate fetal response, more responses were observed in state 2 F. An obvious increase in fetal reactivity to acoustic stimulation was noted in states of wakefulness (states 3 F and 4 F). Comparison between the true and sham stimulations revealed a relatively high level of spontaneous fetal activity (high variation of fetal heart rate and fetal motility) present in states 2 F and 4 F. This must be taken into account in all assessments of fetal responses.(ABSTRACT TRUNCATED AT 250 WORDS)