ABSTRACT
The effect of a moderate heat stress (20 minutes 70°C) on uterine and umbilical artery
blood flow was studied by continuous-wave Doppler ultrasound in 17 women 36 to 37
weeks pregnant. Maternal heart rate increased on average by 26 beats/minute. Maternal
arterial blood pressure did not change during the heat stress but declined slightly
immediately after. The fetal heart rate increased on average by 14 beats/minute by
the end of the exposure. The variability of fetal heart rate was normal in each subject
during the whole experiment and only one subject had a nonreactive tracing during
the heat stress, which returned to normal during the recovery period. The ratio of
the systolic to diastolic velocity in the uterine artery did not change significantly.
Only two subjects had a marked increase in uterine artery vascular resistance; they
had concomitantly a significant fall in the arterial blood pressure. Still, there
was no change in umbilical artery blood flow. The fetuses of healthy pregnant women
are not compromised during or after moderate thermal stress.
