State transitions in uncomplicated pregnancies after term

A behavioural state transition is the time interval between two different behavioural states. In low-risk fetuses, the fetal heart rate pattern (FHRP) is the first variable to change in transitions from 1F to 2F ('non-REM-sleep' to 'REM-sleep') and the last variable to change in transitions from 2F to 1F. This is not the case in IUGR (intra-uterine growth retardation), and absence of a specific order in which behavioural variables are changing might be an indication for a (mild) disturbance of the fetal central nervous system (CNS). We investigated whether state transitions in twelve low risk term fetuses (39-41 weeks post menstrual age, PMA; control group) differ from those in twelve uncomplicated pregnancies > 41 weeks PMA (study group). All subjects underwent one behavioural study in which fetal heart rate pattern, eye and body movements were recorded simultaneously. We recorded 23 transitions from 1F to 2F and 20 from 2F to 1F. Median (range) duration for transitions from 1F to 2F was 85 (10-180) s in the study group, and 60 (10-180) s in the control group. Transitions from 2F to 1F lasted 80 (10-140) and 60 (30-100) s, respectively. In both groups, the FHRP was the first variable to change in transitions from 1F to 2F, however, in transitions from 2F to 1F, no specific order in change of variables could be demonstrated. We conclude that the study of transitions does not distinguish between the term and after term fetuses under optimal conditions. Whether or not the analysis of state transitions can be used to distinguish 'normal' from 'abnormal' fetuses and detect the fetus at risk after term awaits further study.