Doppler Flow Measurement of Uterine and Umbilical Arteries in Heat Stress During Late Pregnancy

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.