ABSTRACT
It has been estimated that as little as a 20% drop in oxygen delivery to the brain can cause a loss of consciousness. While there is a slight reduction in the oxygen-carrying capacity of blood in late pregnancy from 18 to 16 mL/dL of arterial and 13.5 to 12 mL/dL in mixed venous blood, oxygen delivery is not significantly different (868 and 806 mL/min) (15). Several mechanisms maintain adequate cerebral oxygenation and these can be affected by pregnancy.
