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

NCT07326176 | Completed

• 2 other identifiers: GaHPS227176/Z/23/Z
• Study Type: interventional
• Target: 24
• Locations: 1 country
• Sites: 1

Brief Summary

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.

Conditions

Thermally Neutral Condition With Moderate-intensity Work; Warm Condition With Light-intensity Work; Warm Condition With Moderate-intensity Work; Thermally Neutral Condition With Light-intensity Work

Keywords

heat stress; heat strain

Outcome Measures

Primary Outcomes (12)

• 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 Outcomes (8)

• Maternal Skin Temperature

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

• Maternal Heart Rate

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

• Maternal Local Sweat Rate

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

• Maternal Skin Blood Flow

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

• Maternal Arterial Blood Pressure

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

Study Arms (4)

Temperate-Light

OTHER

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

Temperate-Moderate

OTHER

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

Warm-Light

OTHER

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

Warm-Moderate

OTHER

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

Interventions

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.

Temperate-Light; Temperate-Moderate; Warm-Light; Warm-Moderate

Eligibility Criteria

• Age: 18 Years+
• Gender Eligibility Details: Pregnant women
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64), Older Adult (65+)

You may qualify if:

• 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

You may not qualify if:

• 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

Sponsors & Collaborators

• University of Thessaly: lead

Study Sites (1)

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

Trikala, Thessaly, 42100, Greece

Location

Related Publications (2)

• 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.

  PMID: 36495891 BACKGROUND

• 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.

  PMID: 39925648 BACKGROUND

Related Links

• Related Info

MeSH Terms

Conditions

Heat Stress Disorders

Interventions

Hot Temperature

Condition Hierarchy (Ancestors)

Wounds and Injuries

Intervention Hierarchy (Ancestors)

Temperature; Thermodynamics; Physical Phenomena; Weather; Atmosphere; Environment; Ecological and Environmental Phenomena; Biological Phenomena; Meteorological Concepts; Environment and Public Health

Study Officials

• Leonidas Ioannou, PhD

  University of Thessaly

  PRINCIPAL INVESTIGATOR

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: NONE
• Purpose: BASIC SCIENCE
• Intervention Model: CROSSOVER
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Principal Investigator

Study Record Dates

• First Submitted: December 10, 2025
• First Posted: January 8, 2026
• Study Start: May 15, 2024
• Primary Completion: August 15, 2024
• Study Completion: August 15, 2024
• Last Updated: January 8, 2026

Record last verified: 2025-12

Data Sharing

• IPD Sharing: Will not share

Locations

GR (1)