Behavioural states: concomitants, clinical implications and the assessment of the condition of the nervous system

Behavioural states do exist in the human fetus. These states have been called 1F to 4F and resemble states 1 to 4 in the neonate. States 1F and 2F are similar to 'non-REM sleep' or 'quiet sleep' and 'REM-sleep' or 'active sleep', respectively. The fetus spends most of the time in these two states. Each state can be characterized by a particular combination of 3 variables: presence or absence of fetal eye movements and body movements, and fetal heart rate patterns A, B, C and D. From about 36 wk these combinations can be recognized during longer periods without interruptions, and with clear state-transitions. At 32 wk a certain linkage between the three variables is already present but a step-wise increase can be seen between 36 and 38 wk. Fetal breathing, mouthing movements and fetal voiding are state concomitants. Breathing movements are much more regular during state 1F than during state 2F, while the incidence is increased in 2F. It is demonstrated that knowledge of fetal behavioural states is necessary for an adequate interpretation of the fetal heart rate patterns. The concept of behavioural states may be useful for the early detection of disturbances of the developing fetal nervous system. It is therefore concluded that further studies on fetal behaviour have to be 'standardized' for behavioural states.