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

December 23, 2025 updated by: Leonidas G. Ioannou, University of Thessaly
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

Status

Indicates the current recruitment status or the expanded access status.
Completed

Conditions

Conditions

The disease, disorder, syndrome, illness, or injury that is being studied. On ClinicalTrials.gov, conditions may also include other health-related issues, such as lifespan, quality of life, and health risks.

Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.

Study Type

Study Type

Describes the nature of a clinical study. Study types include interventional studies (also called clinical trials), observational studies (including patient registries), and expanded access.
Interventional

Enrollment (Actual)

Enrollment

The number of participants in a clinical study. The "anticipated" enrollment is the target number of participants that the researchers need for the study.
24

Phase

Phase

The stage of a clinical trial studying a drug or biological product, based on definitions developed by the U.S. Food and Drug Administration (FDA). The phase is based on the study's objective, the number of participants, and other characteristics. There are five phases: Early Phase 1 (formerly listed as Phase 0), Phase 1, Phase 2, Phase 3, and Phase 4. Not Applicable is used to describe trials without FDA-defined phases, including trials of devices or behavioral interventions.
  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

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

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Eligibility Criteria

The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

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

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

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

Arms and Interventions

Participant Group / Arm

Participant Group / Arm

A group or subgroup of participants in a clinical trial that receives a specific intervention/treatment, or no intervention, according to the trial's protocol.
Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.
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

Primary Outcome Measures

In a clinical study's protocol, the planned outcome measure that is the most important for evaluating the effect of an intervention/treatment. Most clinical studies have one primary outcome measure, but some have more than one.
Outcome Measure
Measure Description
Time Frame
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).
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
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.
Continuously calculated throughout each 3-hour experimental session (baseline, passive exposure, physical work, and recovery).
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.
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)
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.
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)
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.
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
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.
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
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.
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
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.
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
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.
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)
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.
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)
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.
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)
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.
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

Secondary Outcome Measures

In a clinical study's protocol, a planned outcome measure that is not as important as the primary outcome measure for evaluating the effect of an intervention but is still of interest. Most clinical studies have more than one secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
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.
Continuously recorded throughout each 3-hour experimental session (baseline, passive exposure, physical work, and recovery).
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.
Continuously recorded throughout each 3-hour experimental session (baseline, passive exposure, physical work, and recovery).
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.
Continuously recorded throughout each 3-hour experimental session (baseline, passive exposure, physical work, and recovery).
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.
Continuously recorded throughout each 3-hour experimental session (baseline, passive exposure, physical work, and recovery).
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.
Measured at baseline and every 30 minutes during each 3-hour experimental session.
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.
Measured at baseline and every 30 minutes throughout each 3-hour experimental session (passive exposure, physical work, and recovery).
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.
Measured at baseline and every 30 minutes throughout each 3-hour experimental session (passive exposure, physical work, and recovery).
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.
Measured at baseline and every 30 minutes throughout each 3-hour experimental session (passive exposure, physical work, and recovery).

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Sponsor

The organization or person who initiates the study and who has authority and control over the study.
University of Thessaly

Investigators

Investigators

A researcher involved in a clinical study. Related terms include site principal investigator, site sub-investigator, study chair, study director, and study principal investigator.
  • Principal Investigator: Leonidas Ioannou, PhD, University of Thessaly

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Helpful Links

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

Study Start

The actual date on which the first participant was enrolled in a clinical study. The "anticipated" study start date is the date that the researchers think will be the study start date.
May 15, 2024

Primary Completion (Actual)

Primary Completion

The date on which the last participant in a clinical study was examined or received an intervention to collect final data for the primary outcome measure. Whether the clinical study ended according to the protocol or was terminated does not affect this date. For clinical studies with more than one primary outcome measure with different completion dates, this term refers to the date on which data collection is completed for all the primary outcome measures. The "anticipated" primary completion date is the date that the researchers think will be the primary completion date for the study.
August 15, 2024

Study Completion (Actual)

Study Completion

The date on which the last participant in a clinical study was examined or received an intervention/treatment to collect final data for the primary outcome measures, secondary outcome measures, and adverse events (that is, the last participant's last visit). The "anticipated" study completion date is the date that the researchers think will be the study completion date.
August 15, 2024

Study Registration Dates

First Submitted

First Submitted

The date on which the study sponsor or investigator first submitted a study record to ClinicalTrials.gov. There is typically a delay of a few days between the first submitted date and the record's availability on ClinicalTrials.gov (the first posted date).
December 10, 2025

First Submitted That Met QC Criteria

First Submitted That Met QC Criteria

The date on which the study sponsor or investigator first submits a study record that is consistent with National Library of Medicine (NLM) quality control (QC) review criteria. The sponsor or investigator may need to revise and submit a study record one or more times before NLM's QC review criteria are met. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
December 23, 2025

First Posted (Actual)

First Posted

The date on which the study record was first available on ClinicalTrials.gov after National Library of Medicine (NLM) quality control (QC) review has concluded. There is typically a delay of a few days between the date the study sponsor or investigator submitted the study record and the first posted date.
January 8, 2026

Study Record Updates

Last Update Posted (Actual)

Last Update Posted

The most recent date on which changes to a study record were made available on ClinicalTrials.gov. There may be a delay between when the changes were submitted to ClinicalTrials.gov by the study's sponsor or investigator (the last update submitted date) and the last update posted date.
January 8, 2026

Last Update Submitted That Met QC Criteria

Last Update Submitted That Met QC Criteria

The most recent date on which the study sponsor or investigator submitted changes to a study record that are consistent with National Library of Medicine (NLM) quality control (QC) review criteria. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
December 23, 2025

Last Verified

Last Verified

The most recent date on which the study sponsor or investigator confirmed the information about a clinical study on ClinicalTrials.gov as accurate and current. If a study with a recruitment status of recruiting; not yet recruiting; or active, not recruiting has not been confirmed within the past 2 years, the study's recruitment status is shown as unknown.
December 1, 2025

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

Other Study ID Numbers

Identifiers or ID numbers other than the NCT number that are assigned to a clinical study by the study's sponsor, funders, or others. These numbers may include unique identifiers from other trial registries and National Institutes of Health grant 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

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