Behavioral state organization in normal human term fetuses: the relationship between periods of undefined state and other characteristics of state control.

Repeated alteration in episodes of quiet sleep and active sleep is a basic feature of behavioral state organization in human fetuses. When compared to normal fetuses, at-risk fetuses generally exhibit extended periods of no coincidence (PsNC), that is, associations between state variables that cannot be classified as a sleep state. The purpose of this study was to determine if fetuses with extended PsNC differ in other state measures from fetuses with short PsNC. Fetal heart rate and fetal eye and gross body movements were collected simultaneously on 85 normal human fetuses between 37 and 41 weeks gestation for a total of 9,135 minutes (mean 108.8 +/- 12.7 minutes, range 85-130 minutes). We found that as percent PsNC increased, the frequency (r = 0.464, p < 0.0001) of state changes increased and the time spent in active sleep (r = -0.456, p < 0.0001) and the number of fetuses entering an awake state (chi 2 = 4.26, p < 0.039) decreased. In contrast, percent PsNC was independent of the length of time spent in quiet sleep (r = 0.070, p > 0.05). We interpret these findings as an indication that extended PsNC may be the result of disruption of homeostatic control mechanisms during active sleep.