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Heat stress and fetal risk. Environmental limits for exercise and passive heat stress during pregnancy: a systematic review with best evidence synthesis
  1. Nicholas Ravanelli1,2,
  2. William Casasola1,3,
  3. Timothy English1,
  4. Kate M Edwards4,
  5. Ollie Jay1,2,4
  1. 1 Thermal Ergonomics Laboratory, Faculty of Health Sciences, University of Sydney, Sydney, New South Wales, Australia
  2. 2 School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
  3. 3 Exeter Medical School, University of Exeter, Exeter, UK
  4. 4 Charles Perkins Centre, University of Sydney, Sydney, New South Wales, Australia
  1. Correspondence to Dr Ollie Jay, Exercise and Sports Science, Faculty of Health Sciences, Thermal Ergonomics Laboratory, University of Sydney, NSW 2141, Australia; ollie.jay{at}


Objective Pregnant women are advised to avoid heat stress (eg, excessive exercise and/or heat exposure) due to the risk of teratogenicity associated with maternal hyperthermia; defined as a core temperature (Tcore) ≥39.0°C. However, guidelines are ambiguous in terms of critical combinations of climate and activity to avoid and may therefore unnecessarily discourage physical activity during pregnancy. Thus, the primary aim was to assess Tcore elevations with different characteristics defining exercise and passive heat stress (intensity, mode, ambient conditions, duration) during pregnancy relative to the critical maternal Tcore of ≥39.0°C.

Design Systematic review with best evidence synthesis.

Data sources EMBASE, MEDLINE, SCOPUS, CINAHL and Web of Science were searched from inception to 12 July 2017.

Study eligibility criteria Studies reporting the Tcore response of pregnant women, at any period of gestation, to exercise or passive heat stress, were included.

Results 12 studies satisfied our inclusion criteria (n=347). No woman exceeded a Tcore of 39.0°C. The highest Tcore was 38.9°C, reported during land-based exercise. The highest mean end-trial Tcore was 38.3°C (95% CI 37.7°C to 38.9°C) for land-based exercise, 37.5°C (95% CI 37.3°C to 37.7°C) for water immersion exercise, 36.9°C (95% CI 36.8°C to 37.0°C) for hot water bathing and 37.6°C (95% CI 37.5°C to 37.7°C) for sauna exposure.

Conclusion The highest individual core temperature reported was 38.9°C. Immediately after exercise (either land based or water immersion), the highest mean core temperature was 38.3°C; 0.7°C below the proposed teratogenic threshold. Pregnant women can safely engage in: (1) exercise for up to 35 min at 80%–90% of their maximum heart rate in 25°C and 45% relative humidity (RH); (2) water immersion (≤33.4°C) exercise for up to 45 min; and (3) sitting in hot baths (40°C) or hot/dry saunas (70°C; 15% RH) for up to 20 min, irrespective of pregnancy stage, without reaching a core temperature exceeding the teratogenic threshold.

  • thermoregulation
  • gestation
  • development
  • sweating
  • hyperthermia

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  • Contributors NMR, WC, TE, KME and OJ were involved in the conception and design of the systematic review. NMR, WC and TE were responsible for conducting the systematic search. The selection of studies based on the inclusion criteria was primarily conducted by NMR, WC and TE. When disagreement occurred, all authors critically appraised the study inclusion. NMR and WC completed the Cochrane Risk of Bias 2.0 Tool. Data extraction from the included studies was conducted by NMR and independently confirmed by WC and OJ. All authors interpreted the results. NMR, WC and TE drafted the manuscript. OJ and KME critically revised the manuscript. All authors have approved the final version of the manuscript.

  • Funding NMR is supported by a University of Ottawa Excellence Scholarship, a Natural Sciences and Engineering Research Council Postgraduate Scholarship (PGS-D) and an Endeavour Research Fellowship from the Australian Ministry of Education and Training.

  • Competing interests None declared.

  • Provenance and peer review Commissioned; externally peer reviewed.