Similarities and differences in behavioral state organization during sleep periods in the perinatal infant before and after birth.
The purpose of this study was to determine the degree of consistency in behavioral state organization for 30 low-risk human participants examined as fetuses at 38-40 weeks gestation and again as neonates at approximately 2 weeks postnatal age. Behavioral states were assigned similarly for fetuses and neonates in terms of heart rate pattern and the presence or absence of eye and gross body movements. We found that the time spent in a sleep period was distributed among quiet sleep (QS), active sleep (AS), and indeterminate states in virtually identical proportions for fetuses and neonates. However, the only within-subject consistency between the fetal and neonatal periods was in the duration of complete QS epochs. Fetuses made fewer transitions between QS and AS, but neonates had shorter and more structured AS-->QS transitions. These findings suggest that, whereas central nervous system processes governing QS do not change appreciably, the control of AS undergoes significant changes in the 4 weeks spanning the fetal and neonatal periods. We believe that the duration of enclosed QS epochs provides the only stable measure of behavioral state development between the prenatal and postnatal periods.