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Thermoregulation During Pregnancy: a Controlled Trial Investigating the Risk of Maternal Hyperthermia During Exercise in the Heat

Abstract

Objectives

Despite the well-established benefits of exercise, pregnant women are discouraged from physical activity in hot/humid conditions to avoid hyperthermia (core temperature (Tcore) ≥ 39.0 °C). Recent epidemiological evidence also demonstrates greater risk of negative birth outcomes following heat exposure during pregnancy, possibly due to thermoregulatory impairments. We aimed to determine (1) the risk of pregnant women exceeding a Tcore of 39.0 °C during moderate-intensity exercise in the heat; and (2) if any thermoregulatory impairments are evident in pregnant (P) versus non-pregnant (NP) women.

Methods

Thirty participants (15 pregnant in their second trimester or third trimester) completed two separate exercise-heat exposures in a climate chamber (32 °C, 45%RH). On separate occasions, each participant cycled on a semi-recumbent cycle ergometer for 45 min at a workload representative of a moderate-intensity (1) non-weight-bearing (NON-WB), or (2) weight-bearing (WB) activity. Thermoregulatory responses were monitored throughout.

Results

The highest rectal temperature observed in a pregnant individual was 37.93 °C. Mean end-exercise rectal temperature did not differ between groups (P:37.53 ± 0.22 °C, NP:37.52 ± 0.34 °C, P = 0.954) in the WB trial, but was lower in the P group (P:37.48 ± 0.25 °C, vs NP:37.73 ± 0.38 °C, P = 0.041) in the NON-WB trial. Whole-body sweat loss was unaltered by pregnancy during WB (P:266 ± 62 g, NP:264 ± 77 g; P = 0.953) and NON-WB P:265 ± 51 g, NP:300 ± 75 g; P = 0.145) exercise. Pregnant participants reported higher ratings of thermal sensation (felt hotter) than their non-pregnant counterparts in the WB trial (P = 0.002) but not in the NON-WB trial, (P = 0.079).

Conclusion

Pregnant women can perform 45 min of moderate-intensity exercise at 32 °C, 45%RH with very low apparent risk of excessive maternal hyperthermia. No thermoregulatory impairments with pregnancy were observed.

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Acknowledgements

Daniela S Inoue would like to thank to Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) (2017/03947-0) for their support with her international exchange .

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Correspondence to Ollie Jay.

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No financial support was received for the conduct of this study, or for the preparation or publication of this manuscript.

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The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

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All authors made substantial contributions to either: the conception or design of the study; data acquisition, analysis and/or interpretation; the drafting of the manuscript or critical review of the work for important intellectual content. All authors read approved the final submission.

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The study was approved by the University of Sydney Human Research Ethics Committee (HREC No: 2016/982).

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Smallcombe, J.W., Puhenthirar, A., Casasola, W. et al. Thermoregulation During Pregnancy: a Controlled Trial Investigating the Risk of Maternal Hyperthermia During Exercise in the Heat. Sports Med 51, 2655–2664 (2021). https://doi.org/10.1007/s40279-021-01504-y

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