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.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
NONE
Enrollment
24
A controlled 3-hour environmental chamber protocol consisting of 1 hour of passive seated exposure, 1 hour of treadmill walking at prescribed light or moderate intensities (alternating between 2-3 METs or 3-4 METs every 10 minutes), and 1 hour of seated recovery. Each session was conducted under either temperate (20 °C, 45% relative humidity, shaded) or warm (30 °C, 45% relative humidity, shaded) environmental conditions. Environmental settings, workload intensity, and timing were standardized across all participants.
Dept. of Physical Education and Sport Science, University of Thessaly
Trikala, Thessaly, Greece
Maternal Core Body Temperature
Core body temperature continuously assessed using an ingestible telemetric temperature capsule to quantify maternal thermoregulatory responses to different combinations of environmental heat (20 °C vs 30 °C) and physical workload (light vs moderate).
Time frame: 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
Physiological Strain Index (0-10 scale) calculated from core body temperature and heart rate to quantify overall maternal physiological heat strain under different environmental and workload combinations.
Time frame: Continuously calculated throughout each 3-hour experimental session (baseline, passive exposure, physical work, and recovery).
Fetal Heart Rate
Fetal heart rate assessed using obstetric ultrasound to evaluate fetal cardiovascular responses to maternal exposure to different environmental temperatures and physical workload intensities.
Time frame: 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)
Pulsatility Index of the left and right uterine arteries measured by Doppler ultrasound to assess uteroplacental vascular resistance under different environmental and workload conditions.
Time frame: 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)
Resistive Index of the left and right uterine arteries measured by Doppler ultrasound to assess uteroplacental vascular resistance under different environmental and workload conditions.
Time frame: 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
Pulsatility Index of the umbilical artery measured by Doppler ultrasound to evaluate fetoplacental blood flow in response to maternal heat exposure and physical work.
Time frame: 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
Resistive Index of the umbilical artery measured by Doppler ultrasound to evaluate fetoplacental blood flow in response to maternal heat exposure and physical work.
Time frame: 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
Pulsatility Index of the fetal middle cerebral artery measured by Doppler ultrasound to assess fetal cerebral vascular responses to maternal heat strain.
Time frame: 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
Resistive Index of the fetal middle cerebral artery measured by Doppler ultrasound to assess fetal cerebral vascular responses to maternal heat strain.
Time frame: 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)
Cerebroplacental ratio calculated using artery Doppler measurements to characterize maternal-fetal hemodynamics and fetal strain under different environmental and workload conditions.
Time frame: 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)
Cerebrouterine PI ratio calculated using artery Doppler measurements to characterize maternal-fetal hemodynamics and fetal strain under different environmental and workload conditions.
Time frame: 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)
Uteroplacental:cerebral PI ratio calculated using artery Doppler measurements to characterize maternal-fetal hemodynamics and fetal strain under different environmental and workload conditions.
Time frame: Each 3-hour session: 0 min (baseline), 60 min (end of passive exposure), 120 min (end of physical work), 180 min (end of recovery).
Maternal Skin Temperature
Skin temperature measured at four body sites (chest, upper arm, thigh, lower leg) using iButton sensors and expressed as a weighted mean skin temperature to characterize peripheral thermal responses to environmental heat and physical work.
Time frame: Continuously recorded throughout each 3-hour experimental session (baseline, passive exposure, physical work, and recovery).
Maternal Heart Rate
Maternal heart rate measured using a chest-strap heart rate monitor to assess cardiovascular strain across different environmental (20 °C vs 30 °C) and workload (light vs moderate) conditions.
Time frame: Continuously recorded throughout each 3-hour experimental session (baseline, passive exposure, physical work, and recovery).
Maternal Local Sweat Rate
Local sweat rate measured over the trapezius muscle using a ventilated capsule technique, adjusted for skin area, to quantify sweating responses to environmental heat and physical work.
Time frame: Continuously recorded throughout each 3-hour experimental session (baseline, passive exposure, physical work, and recovery).
Maternal Skin Blood Flow
Skin blood flow assessed using laser Doppler flowmetry at the finger and forearm to characterize peripheral vasodilation in response to environmental heat exposure and physical work.
Time frame: Continuously recorded throughout each 3-hour experimental session (baseline, passive exposure, physical work, and recovery).
Maternal Arterial Blood Pressure
Systolic, diastolic, and mean arterial blood pressure measured intermittently using a standard automated sphygmomanometer to evaluate cardiovascular responses to environmental heat and physical work.
Time frame: Measured at baseline and every 30 minutes during each 3-hour experimental session.
Thermal Sensation
Thermal sensation assessed using a 9-point scale ranging from -4 (extremely cold) to +4 (extremely hot) to quantify participants' perceived body temperature during exposure to different environmental heat and physical workload conditions.
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Time frame: Measured at baseline and every 30 minutes throughout each 3-hour experimental session (passive exposure, physical work, and recovery).
Thermal Comfort
Thermal comfort assessed using a 10-point scale ranging from 1 (comfortable) to 10 (extremely uncomfortable) to evaluate subjective comfort during environmental heat exposure and physical work.
Time frame: Measured at baseline and every 30 minutes throughout each 3-hour experimental session (passive exposure, physical work, and recovery).
Rating of Perceived Exertion (RPE)
Perceived exertion assessed using the Borg 6-20 scale to quantify subjective physical effort during treadmill walking under different environmental and workload conditions.
Time frame: Measured at baseline and every 30 minutes throughout each 3-hour experimental session (passive exposure, physical work, and recovery).