The effect of maternal hyperoxia on behavioral activity in growth-retarded human fetuses.

Thirteen pregnant women who subsequently were delivered of infants with birth weights less than the 3rd percentile were studied for examination of fetal heart rate and fetal activity patients during maternal administration of oxygen at a concentration of 50% or room air for 2 hours. None of the fetuses was acidotic at birth. Maternal transcutaneous PO2 levels increased from 79 +/- 3 mm Hg to 158 +/- 10 mm Hg for the 2 hours of observation. The results indicated that maternal hyperoxia produced sustained fetal breathing activity that was almost 100% higher than that in room air (analysis of variance, p = 0.024). Gross fetal body movements, fetal heart rate accelerations, and fetal heart rate variability increased significantly with increasing observation time (analysis of variance, p less than 0.01), but were not significantly altered by maternal hyperoxia or room air. We conclude that despite significant change in fetal breathing activity, ultrasonographic observation of fetal behavioral activity during maternal hyperoxia could not be used to differentiate severely growth-retarded from normally grown human fetuses. We speculate that altered fetal heart rate and fetal body movement patterns usually associated with intrauterine growth retardation might be related to altered development of the fetal central nervous system and are not reversible during prolonged maternal administration of oxygen.