The effect of acute maternal hypoxia on fetal oxygenation and the umbilical circulation in the sheep.

The mean oxygen consumption was 8.4 +/- 1.9 ml/min/kg in the near-term fetal sheep. In response to acute maternal hypoxia fetal O2 consumption decreased to lower than 50% of the control values. The decrease was rapidly instituted, proportional to the degree of hypoxia, sustained for up to 47 min and stable over this period. With increasing duration of hypoxia, a progressive metabolic acidosis developed. Recovery of oxygen consumption occurred rapidly after hypoxia ceased, though the acidosis was not resolved until 2 h later. Umbilical blood flow was maintained during maternal hypoxia and umbilical arterial and venous pressures increased. A fetal bradycardia invariably accompanied the hypoxia.