What is a notable characteristic of the quiet sleep state in human fetuses?

The quiet sleep state in human fetuses is characterized by no eye movements and occasional startling. During this state, fetal brain activity shows a pattern similar to the sleep cycle observed in newborns and adults. The absence of eye movements indicates a deeper, more restful sleep phase where metabolic and developmental processes can occur without external stimuli causing disturbances.

The potential for occasional startling can be attributed to environmental stimuli or internal sensory processes, reflecting the fetus's neurological responsiveness even in a state of quiet sleep. This can be important for assessing fetal wellbeing and development. In contrast, the other states described involve varying degrees of activity and responsiveness that do not align with the characteristics of quiet sleep.