Ultrasonic evaluation of fetal body movements over twenty-four hours in the human fetus at twenty-four to twenty-eight weeks' gestation.

Continuous 24-hour observations of fetal gross body movements were performed in 20 women between 24 and 28 weeks of gestation by means of real-time ultrasound examination. At 24 to 26 weeks, fetuses moved 13.1% +/- 0.3% of the time, which was not significantly different from the incidence of 12.4% +/- 0.8% at 26 to 28 weeks' gestation. An examination of the number of movements per hour demonstrated that fetuses at 24 to 26 weeks' gestation moved on the average 53.4 +/- 1.6 times/hr, which was significantly different from 26 to 28 weeks' gestation when fetuses made 46.2 +/- 1.4 movements/hr. When examined on an hourly basis, fetuses in both age groups demonstrated a significant increase in the number of movements overnight from 2300 to 0800 hours. Intermovement intervals were also examined. Ninety-nine percent of intervals less than 6 minutes in both age groups contained movement. The longest observed quiescent interval was 24 minutes in both age groups. These data suggest that the incidence of fetal body movements is different than that observed in fetuses during the last 10 weeks of gestation. Fetuses at 24 to 28 weeks' gestation exhibit a diurnal pattern of fetal movement and move more frequently than do older fetuses. However, these movements are of a sporadic nature and relatively short duration. Thus these fetuses do not appear to have well-defined periods of rest and activity.