Increased uterine activity and fetal deterioration during maternal hyperthermia.

The role of hyperthermia in the absence of infection has been investigated in the pregnant baboon. Twenty-three near term animals were used. Catheters were placed in maternal and fetal arteries and thermocouples implanted in maternal colon and fetal esophagus. Maternal temperature was raised to between 41 and 42 degrees Centigrade (C.), by applying external heat. The temperature gradient between fetus and mother (delta T F-M) was 0.47 degree C. under steady-state conditions with maternal temperature at 38 degrees C. and rose to 0.75 degree C. at 42 degrees C. Hyperthermia caused a twofold increase in uterine activity; a metabolic acidosis developed in the mother and a profound acidosis and hypoxia developed in the fetus. There was also a marked fall in blood pressure and an increase in heart rate in both mother and fetus; late deceleration of the fetal heart rate occurred at a higher oxygen level and pHa than has been observed under normothermic conditions.