Concurrence of mouthing movement and rapid eye movement/non-rapid eye movement phases with advance in gestation of the human fetus

To evaluate whether mouthing movement in the human fetus is related to advance in gestational age and whether such movement is concurrent with rapid eye movement or non-rapid eye movement phases, 26 fetuses from 28 to 41 weeks' gestation were observed for 60 continuous minutes with real-time ultrasonography. It was evident that regular mouthing movement every 300 to 600 msec concurred with the non-rapid eye movement period, from 35 weeks' gestation to term. Random mouthing movements that occurred at a wide range of intervals from 300 msec to approximately 525 seconds were observed predominantly during the rapid eye movement period and were unrelated to advance in gestational age. These observations were discussed in relation to biologic implications.