Patterns of human fetal breathing activity at 34 to 35 weeks' gestational age.

Continuous measurements of human fetal breathing movements at 34 to 35 weeks' gestational age were made with an ultrasonic real-time scanner for periods of 24 hours in 11 women. A significant increase occurred in fetal breathing activity during the second and third hour following meals and this pattern apparently followed an increase in maternal plasma glucose concentration. There was a prolonged significant increase in fetal breathing activity between 0100 and 0700 hours. Increases in human fetal breathing activity accompanied by increased gross fetal body movements occurred for periods of 20 to 60 minutes out of every 1.0 to 1.5 hours of observation time. It was concluded that the percentage of time spent breathing by normal fetuses was related to time of day and maternal meals. The alternating changes of fetal activity and inactivity observed may represent biologic changes of sleep state in the human fetus in utero at 34 to 35 weeks' gestational age. It will be important to account for these three patterns of fetal breathing activity in clinical studies which examine the usefulness of fetal breathing movements in assessing fetal health.