Fetal adaptations to spontaneous hypoxemia and responses to maternal oxygen breathing

Circulatory adaptations to spontaneous hypoxemia were assessed with the microsphere method at 119-123 days gestation in ovine fetuses who were subsequently found to be growth retarded. Combined ventricular output tended to be increased and it was redistributed so that oxygen delivery to the heart was increased by over 50%, oxygen delivery to the lung and placenta were decreased, and that to other organs, including the brain, were maintained. Maternal oxygen breathing for 1 h not only reversed these adaptations, but also produced an augmented lung blood flow. Umbilical blood flow was not affected. These findings have clinical implications for the growth-retarded fetus about to undergo the stress of labor.