The effect of maternal hyperoxia on breathing movements, body movements and rest-activity cycles of low-risk human fetuses.

The effects of maternal hyperoxia on fetal breathing and body movements, and on fetal activity state as reflected in the fetal heart rate pattern, were studied in 20 healthy gravida. Fetal breathing and trunk movements were observed by means of real-time ultrasound scanning, and the fetal heart rate was recorded continuously before, during and after 30 min of maternal oxygen inhalation by mask. Maternal transcutaneous oxygen tension (TcPO2) was measured in 9 subjects. The protocol was also carried out in ten of the gravidas with substitution of compressed air for oxygen. Maternal TcPO2 nearly doubled during oxygen breathing in the subjects in whom this was measured. There were no significant changes in the incidence of fetal breathing or trunk movements, or in the distribution of heart rate patterns, during maternal oxygen breathing. Also, no differences were observed in these variables between the oxygen and compressed-air experiments. We conclude that the normal level of fetal oxygenation does not limit fetal activity in uncomplicated pregnancies.