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Completed

NCT Number: NCT07326176

Evaluating Pathophysiological Mechanisms of Acute and Chronic Heat Stress on Maternal and Fetal Health

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.

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Key information

Conditions

Thermally Neutral Condition With Light-intensity Work Heat Stress Disorders Thermally Neutral Condition With Moderate-intensity Work Warm Condition With Light-intensity Work Warm Condition With Moderate-intensity Work Wounds and Injuries

Age range

18 year and older

Sex eligibility

Female

Study type

Interventional

Phase

Not applicable

Primary location

Dept. of Physical Education and Sport Science, University of Thessaly

Trikala, Thessaly, 42100, Greece

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • Healthy pregnant women between 28 and 32 weeks of gestation
  • Singleton pregnancy
  • Habitually heat-acclimatized, defined as daily exposure to outdoor environmental conditions equal to or warmer than those used in the study
  • Able to perform treadmill walking at light and moderate intensities
  • Willing and able to attend all laboratory sessions
  • Provided written informed consent
  • Age 18 years or older

Exclusion criteria

  • Multiple pregnancy (e.g., twins, triplets)
  • Chronic medical conditions, including but not limited to:
  • Hypertension
  • Diabetes
  • HIV
  • Obstetric complications, including:
  • Pre-eclampsia
  • Severe anemia
  • Acute infections, including urinary tract infection
  • Any contraindication to exercise based on the Physical Activity Readiness for Pregnancy (PARmed-X for Pregnancy) checklist
  • Inability to comply with the study procedures or scheduled visits
  • Any condition deemed by investigators to compromise participant safety or data integrity

Treatment and study plan

Heat and Physical Work Exposure Protocol

Other

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.

Primary outcomes

  1. Maternal Core Body Temperature

    Time frame: Continuously recorded throughout each 3-hour experimental session (baseline, 1-hour passive exposure, 1-hour physical work, and 1-hour recovery).

    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).

  2. Maternal Physiological Strain Index

    Time frame: Continuously calculated throughout each 3-hour experimental session (baseline, passive exposure, physical work, and recovery).

    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.

  3. Fetal Heart Rate

    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).

    Fetal heart rate assessed using obstetric ultrasound to evaluate fetal cardiovascular responses to maternal exposure to different environmental temperatures and physical workload intensities.

  4. Uterine Artery Pulsatility Index (PI)

    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).

    Pulsatility Index of the left and right uterine arteries measured by Doppler ultrasound to assess uteroplacental vascular resistance under different environmental and workload conditions.

  5. Uterine Artery Resistive Index (RI)

    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).

    Resistive Index of the left and right uterine arteries measured by Doppler ultrasound to assess uteroplacental vascular resistance under different environmental and workload conditions.

  6. Umbilical Artery Pulsatility Index

    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).

    Pulsatility Index of the umbilical artery measured by Doppler ultrasound to evaluate fetoplacental blood flow in response to maternal heat exposure and physical work.

  7. Umbilical Artery Resistive Index

    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).

    Resistive Index of the umbilical artery measured by Doppler ultrasound to evaluate fetoplacental blood flow in response to maternal heat exposure and physical work.

  8. Middle Cerebral Artery Pulsatility Index

    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).

    Pulsatility Index of the fetal middle cerebral artery measured by Doppler ultrasound to assess fetal cerebral vascular responses to maternal heat strain.

  9. Middle Cerebral Artery Resistive Index

    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).

    Resistive Index of the fetal middle cerebral artery measured by Doppler ultrasound to assess fetal cerebral vascular responses to maternal heat strain.

  10. Composite Maternal-Fetal Hemodynamic Ratios (cerebroplacental ratio)

    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).

    Cerebroplacental ratio calculated using artery Doppler measurements to characterize maternal-fetal hemodynamics and fetal strain under different environmental and workload conditions.

  11. Composite Maternal-Fetal Hemodynamic Ratios (cerebrouterine PI ratio)

    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).

    Cerebrouterine PI ratio calculated using artery Doppler measurements to characterize maternal-fetal hemodynamics and fetal strain under different environmental and workload conditions.

  12. Composite Maternal-Fetal Hemodynamic Ratios (Uteroplacental:cerebral PI ratio)

    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).

    Uteroplacental:cerebral PI ratio calculated using artery Doppler measurements to characterize maternal-fetal hemodynamics and fetal strain under different environmental and workload conditions.

Secondary outcomes

  1. Maternal Skin Temperature

    Time frame: Continuously recorded throughout each 3-hour experimental session (baseline, passive exposure, physical work, and recovery).

    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.

  2. Maternal Heart Rate

    Time frame: Continuously recorded throughout each 3-hour experimental session (baseline, passive exposure, physical work, and recovery).

    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.

  3. Maternal Local Sweat Rate

    Time frame: Continuously recorded throughout each 3-hour experimental session (baseline, passive exposure, physical work, and recovery).

    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.

  4. Maternal Skin Blood Flow

    Time frame: Continuously recorded throughout each 3-hour experimental session (baseline, passive exposure, physical work, and recovery).

    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.

  5. Maternal Arterial Blood Pressure

    Time frame: Measured at baseline and every 30 minutes during each 3-hour experimental session.

    Systolic, diastolic, and mean arterial blood pressure measured intermittently using a standard automated sphygmomanometer to evaluate cardiovascular responses to environmental heat and physical work.

  6. Thermal Sensation

    Time frame: Measured at baseline and every 30 minutes throughout each 3-hour experimental session (passive exposure, physical work, and recovery).

    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.

  7. Thermal Comfort

    Time frame: Measured at baseline and every 30 minutes throughout each 3-hour experimental session (passive exposure, physical work, and recovery).

    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.

  8. Rating of Perceived Exertion (RPE)

    Time frame: Measured at baseline and every 30 minutes throughout each 3-hour experimental session (passive exposure, physical work, and recovery).

    Perceived exertion assessed using the Borg 6-20 scale to quantify subjective physical effort during treadmill walking under different environmental and workload conditions.

Sponsors and collaborators

Lead sponsor

University of Thessaly

Other

Registry information

Acronym: GaHPS

Important dates

Study start
2024
Primary completion
2024
Study completion
2024
First posted
Jan 8, 2026
Registry last updated
Jan 8, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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