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

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 Overview

• Status: Completed
• Conditions: Thermally Neutral Condition With Light-intensity Work; Thermally Neutral Condition With Moderate-intensity Work; Warm Condition With Light-intensity Work; Warm Condition With Moderate-intensity Work
• Intervention / Treatment: Other: Heat and Physical Work Exposure Protocol

• Study Type: Interventional
• Enrollment (Actual): 24
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Greece
  • Thessaly
    • Trikala, Thessaly, Greece, 42100
      • Dept. of Physical Education and Sport Science, University of Thessaly

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

Description

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

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: None (Open Label)

Number of Arms

4

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Other: Temperate-Light; Participants were exposed to a temperate environment (20 °C, 45% relative humidity, shaded) for a 3-hour protocol consisting of 1 hour passive seated exposure, 1 hour of light-intensity treadmill walking (alternating between 2 and 3 METs [Metabolic Equivalents] every 10 minutes), and 1 hour seated recovery.	Other: Heat and Physical Work Exposure Protocol; 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.
Other: Temperate-Moderate; Participants were exposed to a temperate environment (20 °C, 45% relative humidity, shaded) for a 3-hour protocol consisting of 1 hour passive seated exposure, 1 hour of moderate-intensity treadmill walking (alternating between 3 and 4 METs every 10 minutes), and 1 hour seated recovery.	Other: Heat and Physical Work Exposure Protocol; 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.
Other: Warm-Light; Participants were exposed to a warm environment (30 °C, 45% relative humidity, shaded) for a 3-hour protocol consisting of 1 hour passive seated exposure, 1 hour of light-intensity treadmill walking (alternating between 2 and 3 METs every 10 minutes), and 1 hour seated recovery.	Other: Heat and Physical Work Exposure Protocol; 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.
Other: Warm-Moderate; Participants were exposed to a warm environment (30 °C, 45% relative humidity, shaded) for a 3-hour protocol consisting of 1 hour passive seated exposure, 1 hour of moderate-intensity treadmill walking (alternating between 3 and 4 METs every 10 minutes), and 1 hour seated recovery.	Other: Heat and Physical Work Exposure Protocol; 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.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
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).	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.	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.	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.	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.	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.	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.	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.	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.	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.	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.	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.	Each 3-hour session: 0 min (baseline), 60 min (end of passive exposure), 120 min (end of physical work), 180 min (end of recovery).

Secondary Outcome Measures

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

Collaborators and Investigators

• Sponsor: University of Thessaly
• Investigators: Principal Investigator: Leonidas Ioannou, PhD, University of Thessaly

Publications and helpful links

General Publications

• Bonell A, Sonko B, Badjie J, Samateh T, Saidy T, Sosseh F, Sallah Y, Bajo K, Murray KA, Hirst J, Vicedo-Cabrera A, Prentice AM, Maxwell NS, Haines A. Environmental heat stress on maternal physiology and fetal blood flow in pregnant subsistence farmers in The Gambia, west Africa: an observational cohort study. Lancet Planet Health. 2022 Dec;6(12):e968-e976. doi: 10.1016/S2542-5196(22)00242-X.
• Bonell A, G Ioannou L, Sesay A, A Murray K, Bah B, Jeffries D, E Moore S, Vicero-Cabrera A, S Maxwell N, E Hirst J, Tan C, Saucy A, Watters D, Sonko B, Okoh E, Idris Y, Oluwatosin Adefila W, Manneh J, Leigh-Nabou M, Bojang S, Flouris A, Haines A, Prentice A, N Sferruzzi-Perri A. Study protocol for an observational cohort study of heat stress impacts in pregnancy in The Gambia, West Africa. Wellcome Open Res. 2025 Feb 7;9:624. doi: 10.12688/wellcomeopenres.23172.2. eCollection 2024.

Helpful Links

• Related Info

Study record dates

Study Major Dates

• Study Start (Actual): May 15, 2024
• Primary Completion (Actual): August 15, 2024
• Study Completion (Actual): August 15, 2024

Study Registration Dates

• First Submitted: December 10, 2025
• First Submitted That Met QC Criteria: December 23, 2025
• First Posted (Actual): January 8, 2026

Study Record Updates

• Last Update Posted (Actual): January 8, 2026
• Last Update Submitted That Met QC Criteria: December 23, 2025
• Last Verified: December 1, 2025

More Information

Terms related to this study

• Keywords: heat stress; heat strain
• Additional Relevant MeSH Terms: Wounds and Injuries; Heat Stress Disorders; Environment and Public Health; Physical Phenomena; Environment; Ecological and Environmental Phenomena; Biological Phenomena; Thermodynamics; Weather; Atmosphere; Meteorological Concepts; Temperature; Hot Temperature
• Other Study ID Numbers: GaHPS; 227176/Z/23/Z (Other Grant/Funding Number: Wellcome)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Individual participant data (IPD) will not be shared due to the sensitive nature of the data collected from pregnant women and their fetuses and the potential risk of re-identification. De-identified, non-trackable aggregated data supporting the main study findings will be made available after publication.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No