Differential developmental process of respective behavioral states in human fetuses

The presence of behavioral states has been recognized in human fetuses. However, developmental process of fetal behavioral states remains to be clarified. In thirty-one normal pregnant women between 20 and 41 weeks' gestation, fetal movements were examined by using multiple ultrasonic machines. The entire period was divided into eye movement (EM), no eye movement (NEM), and unclassified periods according to the mode of appearance of rapid eye movements. We investigated changes in the ratio of EM and NEM periods and the incidence of various fetal movements in these periods. The ratio of EM periods increased stepwise between 20 and 32 weeks. The difference in the incidence of "startle" and jaw movements between EM and NEM periods was found at 24-27 and 32-35 weeks, respectively. We found a significant decrease in the incidence of total body movements exclusively in NEM periods at 36-39 weeks and a significant increase in the incidence of "rolling" in EM periods at 40-41 weeks. Eye opening was ultrasonographically recognized, providing evidence for awake state in the human fetus. This study revealed the characteristic appearance of fetal movements as related to the presence or absence of EM during the second half of pregnancy, and thereby pointed to differential development process of behavioral states of human fetuses.