Patterns of fetal breathing activity in the human fetus at 24 to 28 weeks of gestation.

Continuous 24-hour observations of fetal breathing were performed in 20 normal, pregnant women between 24 and 28 weeks' gestation by real-time ultrasound. Fetuses made breathing movements approximately 14% of the time. No change in breathing activity after a maternal meal was observed, but a significant increase in the incidence of fetal breathing activity was noted overnight. Fetuses at 24 to 28 weeks' gestation breathed at a rate of 44 breaths per minute, and the longest period of apnea noted was 14 minutes. These data suggest that the pattern and incidence of fetal breathing at 24 to 28 weeks' gestation are different from those of fetuses observed in the last 10 weeks of pregnancy. A maturational process in the control of fetal breathing may explain these observations.