The fetus produces much metabolic heat and loses if mainly via the pla
cental circulation, across a fetomaternal temperature gradient of simi
lar to 0.5 degrees C. During maternal hyperthermia, the risk of noxiou
s fetal hyperthermia is less than expected. The thermal protection app
ears to result from the fefus's own thermal inertia and consequences o
f maternal thermoregulatory strategies.