Behavioural states in normal mature human fetuses.

Behaviour was studied by real time ultrasound in a group of 80 low risk fetuses between 36 and 42 weeks' gestation. There was close linkage of fetal eye movements, somatic movements and heart rate pattern reflecting three different states. Quiescence (state 1F) was characterised by no eye movements, no somatic movements except for the occasional startle, and a fetal heart rate pattern with little baseline variability. There were two active states: state 2F characterised by continuous eye movements, frequent bursts of somatic movements, and wide baseline variability with accelerations with movement, and state 4F characterised by continuous eye movements with almost continuous somatic movements and a sustained tachycardia. These fulfilled criteria for three of four behavioural states previously described in human fetuses. Cycling of quiescent and active states occurred in 77 (96%) of the fetuses within 100 minutes of starting the recording. 2F was the commonest behavioural state, being seen 58% of the time. 1F was seen 30% of the time, and 4F 9% of the time. During the remaining 3% of observation time the behavioural state was indeterminate.