This study examined the effects of environmental heat and physical work on maternal thermoregulation and fetal physiology in late pregnancy. Twenty-four healthy pregnant women at 28-32 weeks of gestation completed four randomized and counterbalanced 3-hour experimental scenarios combining two thermal conditions (temperate 20 °C and warm 30 °C, both at 45% relative humidity, shaded) and two physical workload intensities (light and moderate treadmill walking). Each scenario included 1 hour of passive seated exposure, 1 hour of treadmill walking, and 1 hour of seated recovery. Maternal thermoregulatory, cardiovascular, perceptual, and hydration responses were monitored continuously, while fetal heart rate and Doppler-derived indices of uterine, umbilical, and middle cerebral artery blood flow were assessed at baseline, end of passive exposure, end of work, and end of recovery. The aims of the study were: (1) to characterize maternal physiological and perceptual responses to heat exposure and physical work; (2) to determine whether maternal physiological heat strain directly affects fetal cardiovascular strain and maternal-fetal hemodynamics; and (3) to examine whether maternal characteristics, particularly body mass index and age, influence maternal thermoregulatory responses and fetal susceptibility to heat stress.
Age range
18 Years
Sex
FEMALE
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Maternal Core Body Temperature
Timeframe: Continuously recorded throughout each 3-hour experimental session (baseline, 1-hour passive exposure, 1-hour physical work, and 1-hour recovery).
Maternal Physiological Strain Index
Timeframe: Continuously calculated throughout each 3-hour experimental session (baseline, passive exposure, physical work, and recovery).
Fetal Heart Rate
Timeframe: Each 3-hour session: 0 min (baseline), 60 min (end of passive exposure), 120 min (end of physical work), 180 min (end of recovery).
Uterine Artery Pulsatility Index (PI)
Timeframe: Each 3-hour session: 0 min (baseline), 60 min (end of passive exposure), 120 min (end of physical work), 180 min (end of recovery).
Uterine Artery Resistive Index (RI)
Timeframe: Each 3-hour session: 0 min (baseline), 60 min (end of passive exposure), 120 min (end of physical work), 180 min (end of recovery).
Umbilical Artery Pulsatility Index
Timeframe: Each 3-hour session: 0 min (baseline), 60 min (end of passive exposure), 120 min (end of physical work), 180 min (end of recovery).
Umbilical Artery Resistive Index
Timeframe: Each 3-hour session: 0 min (baseline), 60 min (end of passive exposure), 120 min (end of physical work), 180 min (end of recovery).
Middle Cerebral Artery Pulsatility Index
Timeframe: Each 3-hour session: 0 min (baseline), 60 min (end of passive exposure), 120 min (end of physical work), 180 min (end of recovery).
Middle Cerebral Artery Resistive Index
Timeframe: Each 3-hour session: 0 min (baseline), 60 min (end of passive exposure), 120 min (end of physical work), 180 min (end of recovery).
Composite Maternal-Fetal Hemodynamic Ratios (cerebroplacental ratio)
Timeframe: Each 3-hour session: 0 min (baseline), 60 min (end of passive exposure), 120 min (end of physical work), 180 min (end of recovery).
Composite Maternal-Fetal Hemodynamic Ratios (cerebrouterine PI ratio)
Timeframe: Each 3-hour session: 0 min (baseline), 60 min (end of passive exposure), 120 min (end of physical work), 180 min (end of recovery).
Composite Maternal-Fetal Hemodynamic Ratios (Uteroplacental:cerebral PI ratio)
Timeframe: Each 3-hour session: 0 min (baseline), 60 min (end of passive exposure), 120 min (end of physical work), 180 min (end of recovery).