STATE TRANSITIONS IN UNCOMPLICATED PREGNANCIES AFTER TERM

A behavioural state transition is the time interval between two differ ent behavioural states. In low-risk fetuses, the fetal heart rate patt ern (FHRP) is the first variable to change in transitions from 1F to 2 F('non-REM-sleep' to 'REM-sleep') and the last variable to change in t ransitions from 2F to 1F. This is not the case in IUGR (intra-uterine growth retardation), and absence of a specific order in which behaviou ral variables are changing might be an indication for a (mild) disturb ance of the fetal central nervous system (CNS). We investigated whethe r state transitions in twelve low risk term fetuses (39-41 weeks post menstrual age, PMA; control group) differ from those in twelve uncompl icated pregnancies > 41 weeks PMA (study group). All subjects underwen t one behavioural study in which fetal heart rate pattern, eye and bod y movements were recorded simultaneously. We recorded 23 transitions f rom 1F to 2F and 20 from 2F to 1F. Median (range) duration for transit ions from 1F to 2F was 85 (10-180) s in the study group, and 60 (10-18 0) 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 fi rst variable to change in transitions from 1F to 2F, however, in trans itions from 2F to 1F, no specific order in change of variables could b e demonstrated. We conclude that the study of transitions does not dis tinguish between the term and after term fetuses under optimal conditi ons. Whether or not the analysis of state transitions can be used to d istinguish 'normal' from 'abnormal' fetuses and detect the fetus at ri sk after term awaits further study. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.