Morphology of active sleep--quiet sleep transitions in normal human term fetuses

Periods of no coincidence (PsNC) among state variables appear to be more predictive of neurobehavioral outcome than the amount of time spent in any particular behavioral state. It has recently been suggested that analysis of the ordering of state variables during a state transition may provide results equivalent to full state analysis. If this were the case, then there ought to be a relationship between the duration of PsNC and fetal heart rate (FHR)-fetal eye movement (FEM) sequencing at the time of a state change. To test this hypothesis, we compared full state analysis with analysis of individual state transitions for 52 normal human fetuses between 38 and 42 weeks of gestation. For the study population as a whole, FHR was the first variable to change in 62 (77%) of 81 1F-->2F transitions and FEM was the first variable to change in 50 (63%) of 79 2F-->1F transitions (chi 2 = 67.9, p < 0.001). Ordering of FHR and FEM at the time of a state change was reversed in 8 (67%) of 12 fetuses with PsNC > or = 15% and is only 6 (15%) of 40 fetuses with PsNC < 15% (chi 2 = 12.5, p < 0.001). We conclude that fetuses who exhibit poor state organization more often display a FHR-FEM sequence at the time of a state transition which is opposite that of fetuses with considerably better state control. However, since only one-third of fetuses with reversed FHR-FEM sequencing actually exhibited more than one such episode, it is unlikely that isolated analysis of state transitions will provide a reliable measure of behavioral state organization in the individual fetus.