Temperature gradient between fetus and mother as an index for assessing intrauterine fetal condition.

Temperature gradient between fetus and mother (deltaTF-M) was measured in 29 pregnant baboons. Thermocouples were implanted in the fetal esophagus and the maternal colon, and, in some instances, thermistor probes were also placed in the fetal esophagus, scalp, and shoulder muscle. Under steady-state conditions, the fetal temperature was found to be higher than that of the mother. Temperatures in the fetal esophagus, scalp, and shoulder were 0.47, 0.28, and 0.19 degrees C. respectively, higher than those in the maternal colon. There was an increase in deltaTF-M during acute fetal stress induced by asphyxia, secondary to occlusion of the umbilical cord, maternal aorta, or inferior vena cava, or to acutely increased uterine activity. This increase in deltaTF-M most likely reflects impairment of heat dissipation from the fetus to the maternal compartment. A decreased deltaTF-M was observed when the stress on the fetus was subacute and prolonged. This is probably the result of a diminution of heat production by the fetus as the metabolic rate is lowered during prolonged hypoxia. Ten to 30 minutes after the cessation of vital signs of the fetus, the deltaTF-M became zero.