Heat stress and fetal risk. Environmental limits for exercise and passive heat stress during pregnancy: a systematic review with best evidence synthesis

Sauna therapy in rheumatic diseases: mechanisms, potential benefits, and cautions

Rheumatic diseases (RDs) present a major global health challenge, particularly in aging populations, due to chronic inflammation, progressive joint damage, and impaired mobility. While pharmacologic interventions, such as non-steroidal anti-inflammatory drugs (NSAIDs) and disease-modifying antirheumatic drugs (DMARDs), remain central to RDs management, concerns regarding their side effects and incomplete symptom relief have increased interest in complementary therapies. Sauna therapy, particularly its Finnish and infrared modalities, has emerged as a promising non-pharmacologic intervention with potential anti-inflammatory, musculoskeletal, and cardiovascular benefits. Heat exposure modulates inflammatory pathways by reducing pro-inflammatory agents (TNF-α, CRP, PGE2, LTB4) while promoting IL-10-mediated anti-inflammatory effects. Additionally, sauna therapy mitigates oxidative stress and enhances neuroendocrine regulation, contributing to systemic health benefits. Clinical evidence points to benefits of sauna therapy related to alleviating pain, reducing stiffness, and improving mobility in patients with rheumatoid arthritis (RA), ankylosing spondylitis (AS), and osteoarthritis (OA). Some studies have demonstrated reductions in pain scores and inflammatory markers, improved physical function, and disease stability following infrared sauna exposure. Moreover, cardiovascular advantages of regular sauna use are particularly relevant for RD patients with cardiovascular comorbidities. Given the growing body of evidence supporting its therapeutic potential, sauna therapy represents a viable adjunctive strategy for RD management. Further research is warranted to optimize treatment protocols, assess long-term safety, and delineate patient-specific benefits. Integrating sauna therapy into comprehensive RD care may enhance symptom control, improve quality of life, and reduce reliance on pharmacologic interventions.

Sauna use as a novel management approach for cardiovascular health and peripheral arterial disease

Introduction

Heat therapy (HT), particularly in the form of whole-body sauna bathing, has emerged as a promising intervention for the management of cardiovascular disease (CVD). Passive HT can induce both local and systemic physiological responses, primarily through repeated thermal stress consisting of short-term passive exposure to high temperatures. Such responses closely parallel the physiological adaptations observed during aerobic exercise. Peripheral arterial disease (PAD) poses significant health challenges, impacting millions of individuals worldwide. Supervised exercise is considered a cornerstone therapy for PAD, yet many patients face significant health-related barriers that complicate its broad implementation.

Methods

We conducted a comprehensive review of the literature to explore the therapeutic implications of various HT practices beyond sauna. The review aimed to evaluate the potential use of these practices as adjunctive management strategies for cardiovascular diseases, particularly in patients with PAD.

Results

Recent studies have demonstrated the potential role of HT in alleviating PAD symptoms, improving functional capacity, and reducing cardiovascular and limb events. HT practices might be beneficial as adjunctive management strategies, in addition to or as alternatives to exercise, for management of cardiovascular diseases.

Discussion

This review highlights the potential benefits, underlying mechanisms of action, challenges, and safety considerations associated with HT. We emphasize the importance of exploring HT as a viable option for patients with cardiovascular conditions, particularly those with PAD, who face barriers to traditional exercise regimens.

Associations between exposure to extreme ambient heat and neural tube defects in Georgia, USA: A population-based case-control study

INTRODUCTION

The association between extreme ambient heat exposures during pregnancy and neural tube defects (NTDs) in offspring remains unclear. This study sought to estimate the association between exposure to extreme ambient heat during periconception and NTDs.

METHODS

This population-based case-control study in Georgia, USA (1994-2017) included 825 isolated NTD cases (473 anencephaly, 352 spina bifida) and 3,300 controls matched 1:4 on county of residence and time period of delivery. Daily ambient temperature data were linked to fetal death and birth records by county of residence. Extreme ambient heat exposure was defined as the number of consecutive days the daily apparent temperature exceeded the county-specific 95th percentile (derived over 1980-2010) during an eight-week periconception period. We calculated adjusted odds ratios (aORs) and 95% confidence intervals (CI) using conditional logistic regression models adjusted for maternal age, education, and ethnicity and month and year of last menstrual period.

RESULTS

The aORs for NTDs were 1.09 (95% CI 1.01, 1.17), 1.18 (95% CI 1.03, 1.36), and 1.29 (95% CI 1.04, 1.58) for exposure to 1-2, 3-5, and 6 or more consecutive days with apparent ambient temperatures exceeding the county-specific 95th percentile during periconception, respectively, compared to no days of extreme ambient heat exposure. Weekly analysis of extreme heat exposure indicated consistently elevated odds of offspring NTDs during periconception. These results were largely driven by spina bifida cases.

CONCLUSIONS

Our results highlight potential health threats posed by increasing global average temperatures for pregnant people with implications for increased risk of neural tube defects in their offspring.

Development, validation and reliability of scales and items for heat wave risk assessment of pregnant women

INTRODUCTION

The 1.2 °C rise of global ambient temperature since the pre-industrial era has led to an increase the intensity and frequency of heatwaves. Given the heightened vulnerability of pregnant women to heat stress, there is an urgent need for tools which accurately assess the knowledge, risk, and perception of pregnant woman toward heatwaves, enabling effective policy actions. In this research, we developed and validated tools to evaluate pregnant women's perceptions of heat wave risks and behaviors.

METHOD

We developed 50 items across seven constructs using the Health Belief Model, identified through a systematic literature review. The constructs comprised 8 Knowledge(K) items, 4 in Perceived Vulnerability (PV), 5 in Perceived Severity (PS), 6 in Perceived Benefit (PB), 4 in Perceived Barrier (PBa), 5 in Cue to Action(Cu) and 18 in Adaptation(A). Cognitive testing was performed with a separate group of pregnant women(n = 20). The tested tools were then administered to 120 pregnant women residing during the spring-summer 2023. Construct validation utilized exploratory factor analysis.

RESULTS

The Principal Axis Factoring Method was employed in the EFA with oblimin rotation for 51 items, considering communality > 0.20, and aiming to extract three factors. Across the three factors with Cronbach's alpha > 0.70, a total of 11 items were distributed. Factor 1 included Perceived Severity (PS1, PS2, PS3 and PS5); Factor 2 included Cue to Action (Cu1, Cu2, Cu3, and Cu4); and Factor 3 encompassed Perceived Vulnerability (PV1, PV2, PV4). Only two of the retained items had factor loadings > 0.50, namely PV4 and PS5. Consequently, the three constructs measuring Perceived Severity, Cues to Action, and Perceived Vulnerability using the HBM among pregnant women were deemed valid.

CONCLUSION

Our study has successfully validated a highly reliable tool which stands ready for application in assessing pregnant women's risk perception regarding heatwaves.

Balancing benefits and risks of exercise in pregnancy: a qualitative analysis of social media discussion

Exercise improves pregnancy outcomes, but few pregnant individuals meet physical activity guidelines. The main objective of this study was to explore the perception of exercise during pregnancy using posts and comments on Reddit, a large social media platform. Relevant user-generated posts and comments were identified on Reddit by searching systematically for a combination of keywords related to pregnancy and exercise. A dataset of 120 posts and 2892 comments was randomly selected for reflexive thematic analysis. Three themes relating to perceptions of benefits and risks to exercise in pregnancy and how they influence decision-making were generated: (1) perceived benefits of exercise: 'We all know that exercise is good for us'; (2) perceived risks of exercise: Exercise as 'off limits'; and (3) information seeking and decision-making: 'I'm kinda stumped on exercise'. While the benefits of exercise during pregnancy are well recognised among Reddit users, perceived risks significantly influence their decisions to start, continue, adjust or stop exercising. Healthcare providers play a crucial role in guiding these exercise choices, emphasising the need for them to provide evidence-based advice and support pregnant individuals in achieving optimal physical activity levels. Addressing misinformation and providing supportive counselling can help pregnant individuals navigate the complexities of exercise during this critical period.

Cool mama: Temperature regulation during high-intensity interval running in pregnant elite and recreational athletes

Background

Regular exercise during pregnancy is beneficial, but athletes often exceed the recommended 150 min of moderate-intensity activity, incorporate high-intensity exercises. The upper limit for exercise intensity and duration on fetal and maternal safety remains uncertain. A concern is a maternal core body temperature of >39.0 °C, potentially increase the risk of heat-related fetal malformations and complications during pregnancy. Blood flow redirection for thermoregulation could compromise fetal cardiovascular function, increasing the risk of miscarriage and preterm labor. This study evaluated whether pregnant women (gestational weeks 25-35) were at risk of exceeding a core body temperature of 39.0 °C during high-intensity running. We also investigated effects on skin temperature, fluid loss, and thermal sensation, comparing pregnant athletes to non-pregnant controls.

Methods

In this comparative cross-sectional study, 30 elite and recreational athletes (pregnant n = 15) completed up to five high-intensity treadmill-intervals. Core and skin temperature were continuously measured. Body weight was utilized to calculate the amount of fluid loss.

Results

Highest core body temperature were 38.76 °C and 39.56 °C in one pregnant and non-pregnant participant, respectively. Pregnant participants had lower core body temperatures (mean difference -0.47 °C, p ≤ 0.001) initially and a smaller increase (0.10 °C, p ≤ 0.003) during later intervals compared with the non-pregnant controls. Pregnant participants also showed a greater increase in skin temperature (4.08 ± 0.72 °C vs. 3.25 ± 0.86 °C, p = 0.008) and fluid loss (0.81 ± 0.19 L vs. 0.50 ± 0.12 L, p˂0.001).

Conclusion

Physiological changes in pregnancy may enhance thermoregulation, indicating that high-intensity interval runs are unlikely to pose a risk of exceeding a core body temperature of 39 °C for pregnant athletes.

Climate change, air pollution and maternal and newborn health: An overview of reviews of health outcomes

Background

Climate change represents a fundamental threat to human health, with pregnant women and newborns being more susceptible than other populations. In this review, we aimed to describe the current landscape of available epidemiological evidence on key climate risks on maternal and newborn health (MNH).

Methods

We sought to identify published systematic and scoping reviews investigating the impact of different climate hazards and air pollution on MNH outcomes. With this in mind, we developed a systematic search strategy based on the concepts of 'climate/air pollution hazards, 'maternal health,' and 'newborn health,' with restrictions to reviews published between 1 January 2010 and 6 February 2023, but without geographical or language restriction. Following full text screening and data extraction, we synthesised the results using narrative synthesis.

Results

We found 79 reviews investigating the effects of climate hazards on MNH, mainly focussing on outdoor air pollution (n = 47, 59%), heat (n = 24, 30%), and flood/storm disasters (n = 7, 9%). Most were published after 2015 (n = 60, 76%). These reviews had consistent findings regarding the positive association of exposure to heat and to air pollution with adverse birth outcomes, particularly preterm birth. We found limited evidence for impacts of climate-related food and water security on MNH and did not identify any reviews on climate-sensitive infectious diseases and MNH.

Conclusions

Climate change could undermine recent improvements in maternal and newborn health. Our review provides an overview of key climate risks to MNH. It could therefore be useful to the MNH community to better understand the MNH needs for each climate hazard and to strengthen discussions on evidence and research gaps and potential actions. Despite the lack of comprehensive evidence for some climate hazards and for many maternal, perinatal, and newborn outcomes, we observed repeated findings of the impact of heat and air pollutants on birth outcomes, particularly preterm birth. It is time for policy dialogue to follow to specifically design climate policy and actions to protect the needs of MNH.

Environmental Exposures and Risks During Pregnancy

The Women in Wilderness Medicine Research Committee of the Wilderness Medical Society conducted a narrative review to address considerations for pregnant individuals in wilderness environments. There is limited evidence behind many opinion-based recommendations on the safety of various environmental exposures in pregnancy. The authors reviewed the literature for the best available evidence, including observational studies, case series, limited controlled trials, and extrapolation from physiological data, as well as evaluating expert consensus statements. The benefits of exposure to natural environments include better pregnancy outcomes and improved maternal mental and physical health. Risks are similar to nonpregnant individuals with the added risks associated with maternal-fetal physiology in wilderness environments and difficulties of evacuation. This narrative review discusses pregnancy-specific concerns in extreme environments, including high altitude, hypothermia, hyperthermia, lightning strikes, envenomations, and common outdoor exposures.

Impacts of heat exposure in utero on long-term health and social outcomes: a systematic review

BACKGROUND

Climate change, particularly global warming, is amongst the greatest threats to human health. While short-term effects of heat exposure in pregnancy, such as preterm birth, are well documented, long-term effects have received less attention. This review aims to systematically assess evidence on the long-term impacts on the foetus of heat exposure in utero.

METHODS

A search was conducted in August 2019 and updated in April 2023 in MEDLINE(PubMed). We included studies on the relationship of environmental heat exposure during pregnancy and any long-term outcomes. Risk of bias was assessed using tools developed by the Joanna-Briggs Institute, and the evidence was appraised using the GRADE approach. Synthesis without Meta-Analysis (SWiM) guidelines were used.

RESULTS

Eighteen thousand six hundred twenty one records were screened, with 29 studies included across six outcome groups. Studies were mostly conducted in high-income countries (n = 16/25), in cooler climates. All studies were observational, with 17 cohort, 5 case-control and 8 cross-sectional studies. The timeline of the data is from 1913 to 2019, and individuals ranged in age from neonates to adults, and the elderly. Increasing heat exposure during pregnancy was associated with decreased earnings and lower educational attainment (n = 4/6), as well as worsened cardiovascular (n = 3/6), respiratory (n = 3/3), psychiatric (n = 7/12) and anthropometric (n = 2/2) outcomes, possibly culminating in increased overall mortality (n = 2/3). The effect on female infants was greater than on males in 8 of 9 studies differentiating by sex. The quality of evidence was low in respiratory and longevity outcome groups to very low in all others.

CONCLUSIONS

Increasing heat exposure was associated with a multitude of detrimental outcomes across diverse body systems. The biological pathways involved are yet to be elucidated, but could include epigenetic and developmental perturbations, through interactions with the placenta and inflammation. This highlights the need for further research into the long-term effects of heat exposure, biological pathways, and possible adaptation strategies in studies, particularly in neglected regions. Heat exposure in-utero has the potential to compound existing health and social inequalities. Poor study design of the included studies constrains the conclusions of this review, with heterogenous exposure measures and outcomes rendering comparisons across contexts/studies difficult.

TRIAL REGISTRATION

PROSPERO CRD 42019140136.

Perceived challenges and barriers for females working in the heat

Given rising temperatures, globally, heat exposures and catastrophic heat illnesses are a major concern in laborer and industrial sectors. The purpose of this study was to evaluate the perceptions of females laboring in the heat regarding challenges and barriers encountered in their respective industries while working in the heat. A consensual qualitative research (CQR) design was employed to gain information related to participant occupational and job characteristics, feelings while working in the heat, adjustments made by employers when they work in the heat, and their experience working in the heat specific to their identified sex. Females were eligible to participate if they were currently employed in an environment that required them to work in the heat. Twelve females participated in a single, 45-60 min one-on-one semi-structured interview. Participants reported working in the manufacturing, agriculture, tourism, and railroad industries. Upon completion of data analysis, one primary theme was identified: heat stress mitigation strategies, which were further broken down into two subthemes of formal strategies provided by the employer and informal strategies driven by the employees. Participants indicated there was a lack of heat stress prevention strategies implemented by their employers, which resulted in employees creating their own strategies to protect themselves and their coworkers from heat stress. Results indicated there are limited heat stress prevention strategies that are provided in industries that include females working in the heat. Unique considerations should be made to protect this population from the dangers of heat stress and must go beyond workers protecting themselves.

Heat Stress-Induced Fetal Intrauterine Growth Restriction Is Associated with Elevated LPS Levels Along the Maternal Intestine-Placenta-Fetus Axis in Pregnant Mice

The exacerbation of the greenhouse effect has made heat stress (HS) an important risk factor for the occurrence of intrauterine growth restriction (IUGR). The experiment aims to uncover the effects of maternal HS on IUGR and its mechanisms. The results showed that HS leads to decreased maternal and fetal birth weights, accompanied by increased serum oxidative stress and cortisol levels. Moreover, HS inflicted significant damage to both the intestinal and placental barriers, altering maternal gut microbiota and increasing intestinal LPS levels. As a result, LPS levels increased in maternal serum, placenta, and fetus. Furthermore, HS damaged the intestinal structure, intensifying inflammation and disrupting the redox balance. The placenta exposed to HS exhibited changes in the placental structure along with disrupted angiogenesis and decreased levels of nutritional transporters. Additionally, the leakage of LPS triggered placental JNK and ERK phosphorylation, ultimately inducing severe placental inflammation and oxidative stress. This study suggests that LPS translocation from the maternal intestine to the fetus, due to a disrupted gut microbiota balance and compromised intestinal and placental barrier integrity, may be the primary cause of HS-induced IUGR. Furthermore, increased LPS leakage leads to placental inflammation, redox imbalance, and impaired nutrient transport, further restricting fetal growth.

The risk of miscarriage is associated with ambient temperature: evidence from coastal Bangladesh

Background

Exposure to high ambient temperature is reported to cause adverse pregnancy outcomes. However, considering myriad temperature and climatic conditions as well as different contextual factors, the paucity of studies from the developing regions impedes the development of a clear understanding of the heat-pregnancy outcome relationship.

Materials and methods

This study was conducted in Chakaria, a coastal region of Bangladesh, where International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b) administers a health and demographic surveillance system (HDSS). The surveillance workers visit the households every three months as a part of the routine surveillance activity. Between 2012 and 2020, the surveillance workers documented histories of 23,482 pregnancies among 13,376 women and the women were followed up for their pregnancy outcomes. The temperature records were obtained from the Bangladesh Meteorological Department's weather station at Cox's Bazar. The dates of pregnancy outcome were linked with the daily average temperature on the day of pregnancy outcome. A logistic regression model was employed to examine the relationship between temperature and the incidence of miscarriage.

Results

Out of 23,482 pregnancy outcomes, 3.7% were induced abortions. Among the remaining 22,624 pregnancy outcomes, 86.2% were live births, 10.7% were miscarriages and 3.1% were stillbirths. Miscarriages peaked between 8-14 weeks of gestation and varied according to temperature. For women exposed to temperatures between 28°C and 32°C, the risk of miscarriage was 25% greater (adjusted OR 1.25, 95% CI 1.07-1.47) compared to those exposed to temperatures from 16°C to 21°C.

Conclusion

The study establishes a connection between miscarriage and high ambient temperatures in a coastal region of Bangladesh. Implementing timely and appropriate adaptation strategies to prevent miscarriages is of paramount importance for a densely populated country like Bangladesh.

A Comprehensive Review on Hot Ambient Temperature and its Impacts on Adverse Pregnancy Outcomes

INTRODUCTION

High workplace/ambient temperatures have been associated with Adverse Pregnancy Outcomes (APO). Millions of women working in developing nations suffer due to the rising temperatures caused by climate change. There are few pieces of research linking occupational heat stress to APO, and fresh evidence is required.

METHODOLOGY

We used databases including PubMed, Google Scholar, and Science Direct to search for research on high ambient/workplace temperatures and their effects. Original articles, newsletters, and book chapters were examined. The literature we analysed was categorised as follows: Heat, strain, and physical activity harming both mother and fetus. After categorising the literature, it was examined to identify the major results.

RESULTS

We found a definite association between heat stress and APOs such as miscarriages, premature birth, stillbirth, low birthweight, and congenital abnormalities in 23 research articles. Our work provides important information for future research into the biological mechanisms that create APOs and various prevention measures.

CONCLUSION

Our data suggest that temperature has long-term and short-term effects on maternal and fetal health. Though small in number, this study stressed the need for bigger cohort studies in tropical developing countries to create evidence for coordinated policies to safeguard pregnant women.

High-intensity exercise during pregnancy – A position paper by the European Board and College of Obstetrics and Gynaecology (EBCOG)

Most guidelines recommend regular physical exercise to all pregnant women. However, because of the anatomical and physiological changes which occur during pregnancy, high-intensity exercise and forms of extreme sports can place the pregnant woman and her fetus at risk of harm.

A feasibility study of the use of UmbiFlow™ to assess the impact of heat stress on fetoplacental blood flow in field studies

OBJECTIVE

To evaluate the use of UmbiFlow™ in field settings to assess the impact of heat stress on umbilical artery resistance index (RI).

METHODS

This feasibility study was conducted in West Kiang, The Gambia, West Africa; a rural area with increasing exposure to extreme heat. We recruited women with singleton fetuses who performed manual tasks (such as farming) during pregnancy to an observational cohort study. The umbilical artery RI was measured at rest, and during and at the end of a typical working shift in women at 28 weeks or more of pregnancy. Adverse pregnancy outcomes (APO) were classified as stillbirth, preterm birth, low birth weight, or small for gestational age, and all other outcomes as normal.

RESULTS

A total of 40 participants were included; 23 normal births and 17 APO. Umbilical artery RI demonstrated a nonlinear relationship to heat stress, with indication of a potential threshold value for placental insufficiency at 32°C by universal thermal climate index and 30°C by wet bulb globe temperature.

CONCLUSIONS

The Umbiflow device proved to be an effective field method for assessing placental function. Dynamic changes in RI may begin to explain the association between extreme heat and APO with an identified threshold of effect.

Environmental heat stress on maternal physiology and fetal blood flow in pregnant subsistence farmers in The Gambia, west Africa: an observational cohort study

BACKGROUND

Anthropogenic climate change has caused extreme temperatures worldwide, with data showing that sub-Saharan Africa is especially vulnerable to these changes. In sub-Saharan Africa, women comprise 50% of the agricultural workforce, often working throughout pregnancy despite heat exposure increasing the risk of adverse birth outcomes. In this study, we aimed to improve understanding of the pathophysiological mechanisms responsible for the adverse health outcomes resulting from environmental heat stress in pregnant subsistence farmers. We also aimed to provide data to establish whether environmental heat stress also has physiological effects on the fetus.

METHODS

We conducted an observational cohort study in West Kiang, The Gambia, at the field station for the Medical Research Council Unit The Gambia at London School of Hygiene & Tropical Medicine (named the MRC Keneba field station). Pregnant women who were aged 16 years or older and who were at <36 weeks' gestation of any gravida or parity were invited to participate in the study. Participants were eligible if they were involved in agricultural or related manual daily tasks of living. Participants were ineligible if they refused to provide consent, had multiple pregnancies (eg, if they had twins), were acutely unwell, or were diagnosed with pre-eclampsia or eclampsia. Heat stress was measured by wet bulb globe temperature (WBGT) and by using the universal thermal climate index (UTCI), and maternal heat strain was directly measured by modified physiological strain index calculated from heart rate and skin temperature. Outcome measures of fetal heart rate (FHR) and fetal strain (defined as a FHR >160 beats per min [bpm] or <115 bpm, or increase in umbilical artery resistance index) were measured at rest and during the working period. Multivariable repeated measure models (linear regression for FHR, and logistic regression for fetal strain) were used to evaluate the association of heat stress and heat strain with acute fetal strain.

FINDINGS

Between Aug 26, 2019, and March 27, 2020, 92 eligible participants were recruited to the study. Extreme heat exposure was frequent, with average exposures of WBGT of 27·2°C (SD 3·6°C) and UTCI equivalent temperature of 34·0°C (SD 3·7°C). The total effect of UTCI on fetal strain resulted in an odds ratio (OR) of 1·17 (95% CI 1·09-1·29; p<0·0001), with an adjusted direct effect of OR of 1·12 (1·03-1·21; p=0·010) with each 1°C increase in UTCI. The adjusted OR of maternal heat strain on fetal strain was 1·20 (1·01-1·43; p=0·038), using the UTCI model, with each unit increase.

INTERPRETATION

Data from our study show that decreasing maternal exposure to heat stress and heat strain is likely to reduce fetal strain, with the potential to reduce adverse birth outcomes. Further work that explores the association between heat stress and pregnancy outcomes in a variety of settings and populations is urgently needed to develop effective interventions.

FUNDING

The Wellcome Trust.

Human temperature regulation under heat stress in health, disease, and injury

The human body constantly exchanges heat with the environment. Temperature regulation is a homeostatic feedback control system that ensures deep body temperature is maintained within narrow limits despite wide variations in environmental conditions and activity-related elevations in metabolic heat production. Extensive research has been performed to study the physiological regulation of deep body temperature. This review focuses on healthy and disordered human temperature regulation during heat stress. Central to this discussion is the notion that various morphological features, intrinsic factors, diseases, and injuries independently and interactively influence deep body temperature during exercise and/or exposure to hot ambient temperatures. The first sections review fundamental aspects of the human heat stress response, including the biophysical principles governing heat balance and the autonomic control of heat loss thermoeffectors. Next, we discuss the effects of different intrinsic factors (morphology, heat adaptation, biological sex, and age), diseases (neurological, cardiovascular, metabolic, and genetic), and injuries (spinal cord injury, deep burns, and heat stroke), with emphasis on the mechanisms by which these factors enhance or disturb the regulation of deep body temperature during heat stress. We conclude with key unanswered questions in this field of research.

Sports Obstetrics: Implications of Pregnancy in Elite Sportswomen, a Narrative Review

Increasing numbers of females are participating in elite sports, with a record number having competed at the Tokyo Olympic Games. Importantly, the ages of peak performance and fertility are very likely to coincide; as such, it is inevitable that pregnancy will occur during training and competition. Whilst there is considerable evidence to promote regular exercise in pregnancy, with benefits including a reduction in hypertensive disorders, gestational diabetes, and reduced rates of post-natal depression, few studies have been conducted which include elite athletes. Indeed, there are concerns that high-intensity exercise may lead to increased rates of miscarriage and preterm labour, amongst other pregnancy-related complications. There is minimal guidance on the obstetric management of athletes, and consequently, healthcare professionals frequently adopt a very conservative approach to managing such people. This narrative review summarises the evidence on the antenatal, intrapartum, and postpartum outcomes in elite athletes and provides recommendations for healthcare providers, demonstrating that generally, pregnant athletes can continue their training, with a few notable exceptions. It also summarises the physiological changes that occur in pregnancy and reviews the literature base regarding how these changes may impact performance, with benefits arising from pregnancy-associated cardiovascular adaptations at earlier gestations but later changes causing an increased risk of injury and fatigue.

Physiological mechanisms of the impact of heat during pregnancy and the clinical implications: review of the evidence from an expert group meeting

Many populations experience high seasonal temperatures. Pregnant women are considered vulnerable to extreme heat because ambient heat exposure has been linked to pregnancy complications including preterm birth and low birthweight. The physiological mechanisms that underpin these associations are poorly understood. We reviewed the existing research evidence to clarify the mechanisms that lead to adverse pregnancy outcomes in order to inform public health actions. A multi-disciplinary expert group met to review the existing evidence base and formulate a consensus regarding the physiological mechanisms that mediate the effect of high ambient temperature on pregnancy. A literature search was conducted in advance of the meeting to identify existing hypotheses and develop a series of questions and themes for discussion. Numerous hypotheses have been generated based on animal models and limited observational studies. There is growing evidence that pregnant women are able to appropriately thermoregulate; however, when exposed to extreme heat, there are a number of processes that may occur which could harm the mother or fetus including a reduction in placental blood flow, dehydration, and an inflammatory response that may trigger preterm birth. There is a lack of substantial evidence regarding the processes that cause heat exposure to harm pregnant women. Research is urgently needed to identify what causes the adverse outcomes in pregnancy related to high ambient temperatures so that the impact of climate change on pregnant women can be mitigated.

Extreme Heat and Pregnancy Outcomes: A Scoping Review of the Epidemiological Evidence

BACKGROUND

Extreme heat caused by climate change is a major public health concern, disproportionately affecting poor and racialized communities. Gestational heat exposure is a well-established teratogen in animal studies, with a growing body of literature suggesting human pregnancies are similarly at risk. Characterization of extreme heat as a pregnancy risk is problematic due to nonstandard definitions of heat waves, and variable study designs. To better focus future research in this area, we conducted a scoping review to assess the effects of extreme heat on pregnancy outcomes.

METHODS

A scoping review of epidemiological studies investigating gestational heat-exposure and published 2010 and 2020, was conducted with an emphasis on study design, gestational windows of sensitivity, adverse pregnancy outcomes and characterization of environmental temperatures.

RESULTS

A sample of 84 studies was identified, predominantly set in high-income countries. Preterm birth, birthweight, congenital anomalies and stillbirth were the most common pregnancy outcome variables. Studies reported race/ethnicity and/or socioeconomic variables, however these were not always emphasized in the analysis.

CONCLUSION

Use of precise temperature data by most studies avoided pitfalls of imprecise, regional definitions of heat waves, however inconsistent study design, and exposure windows are a significant challenge to systematic evaluation of this literature. Despite the high risk of extreme heat events and limited mitigation strategies in the global south, there is a significant gap in the epidemiological literature from these regions. Greater consistency in study design and exposure windows would enhance the rigor of this field.

Physical exercise in pregnancy: benefits, risks and prescription

OBJECTIVES

The aim of this article is to provide a comprehensive literature review, gathering the strongest evidence about the risks and benefits and the prescription of physical exercise during pregnancy.

CONTENT

Regular physical exercise during pregnancy is associated with numerous benefits. In general women are not adequately advised on this matter. Along with their concerns regarding the potential associated risks, it contributes to the abandonment or refusal to start exercising during pregnancy. A systematic review was conducted in MEDLINE including articles considered to have the highest level of scientific evidence. Fifty-seven articles, including 32 meta-analysis, 9 systematic reviews and 16 randomized controlled trials were included in the final literature review.

SUMMARY

Exercise can help preventing relevant pregnancy related disorders, such as gestational diabetes, excessive gestational weight gain, hypertensive disorders, urinary incontinence, fetal macrosomia, lumbopelvic pain, anxiety and prenatal depression. Exercise is not related with an increased risk of maternal or perinatal adverse outcomes. Compliance with current guidelines is sufficient to achieve the main benefits, and exercise type and intensity should be based on woman's previous fitness level.

OUTLOOK

Exercise in pregnancy is safe for both mother and fetus, contributing to prevent pregnancy related disorders. Exercise type and intensity should be adapted to woman's previous fitness level, medical history and characteristics of the ongoing pregnancy.

Sauna use as a lifestyle practice to extend healthspan

Sauna use, sometimes referred to as "sauna bathing," is characterized by short-term passive exposure to high temperatures, typically ranging from 45 °C to 100 °C (113 °F to 212 °F), depending on modality. This exposure elicits mild hyperthermia, inducing a thermoregulatory response involving neuroendocrine, cardiovascular, and cytoprotective mechanisms that work in a synergistic fashion in an attempt to maintain homeostasis. Repeated sauna use acclimates the body to heat and optimizes the body's response to future exposures, likely due to the biological phenomenon known as hormesis. In recent decades, sauna bathing has emerged as a probable means to extend healthspan, based on compelling data from observational, interventional, and mechanistic studies. Of particular interest are the findings from large, prospective, population-based cohort studies of health outcomes among sauna users that identified strong dose-dependent links between sauna use and reduced morbidity and mortality. This review presents an overview of sauna practices; elucidates the body's physiological response to heat stress and the molecular mechanisms that drive the response; enumerates the myriad health benefits associated with sauna use; and describes sauna use concerns.

Ambient heat and stillbirth in Northern and Central Florida

BACKGROUND

Elevated temperature is well-recognized as a health hazard, and may be particularly harmful to pregnant women, including increasing risk of stillbirth. We conducted a study in Northern and Central Florida, an area prone to periodic extreme heat but with significant seasonal variation, focusing on the most socioeconomically vulnerable populations least able to mitigate the impact of heat.

METHODS

We obtained electronic health records data from the OneFlorida Data Trust for the period 2012-2017, with 1876 stillbirths included in the analysis. We used a case-crossover design to examine the risk of stillbirth associated with acute exposures to elevated heat prior to the outcome, contrasting the case period (the week preceding the stillbirth) with a control period (the week prior to the case period and the week after the stillbirth). Average heat index and maximum warning level during the case and control periods of each woman were assigned by ZIP code. Conditional logistic regression models were used to assess the association between stillbirth and heat exposure, controlling for PM_2.5 and O₃.

RESULTS

The adjusted odds ratio showed no overall association with stillbirth except for a weak association for exposure above the 90th percentile which was larger among the most socioeconomically deprived and non-Hispanic Black women. In the hot months, there was a clear association for all indices of heat exposure, but largest again for the most socioeconomically deprived population (aOR = 2.4, 95% CI: 1.2-5.2 in the 4th vs. 1st quartile) and among non-Hispanic Black women (aOR = 1.8, 95% CI: 1.0-3.2 in the 4th vs. 1st quartile).

CONCLUSIONS

Our results provide further evidence that elevated ambient heat is related to stillbirth and encourage a focus on the most susceptible individuals and possible clinical pathways.

Heat loss responses at rest and during exercise in pregnancy: A scoping review

BACKGROUND

The teratogenic risk associated with maternal hyperthermia (i.e., core temperature ≥39.0 °C) has been a crucial motive in understanding thermoregulatory responses in pregnancy. To date, a substantial number of studies have focused on core temperature responses in a wide range of exercise intensities, duration, and ambient temperatures. Fortunately, none have reported core temperatures exceeding 39.0 °C. Nonetheless, there are limited studies that have provided substantial insight into both dry and evaporative heat loss mechanisms involved in facilitating the maintenance of core temperature (≥39.0 °C) during heat stress in pregnant women. The purpose of this scoping review was to summarize the available literature that has assessed heat loss responses in studies of human pregnancy.

METHODS

A search strategy was developed combining the terms pregnancy, thermoregulation, and adaptation. A systematic search was performed in the following databases: PubMed, Embase, Scopus, and ProQuest. Studies eligible for inclusion included pregnant women between the ages of 18-40 years old, and at least one measurement of the following: sweating, blood flow, skin temperature, and behavioural responses. Retrieved data were categorized as evaporative (sweating), dry or behavioural heat loss responses and summarized narratively.

RESULTS

Thirty-three studies were included in this review (twenty-nine measured physiological responses and four measured behavioural responses). Studies suggest that during exercise, evaporative (sweating) and dry (skin blood flow and temperature) heat loss responses increase from early to late pregnancy in addition to greater cardiac output, blood volume and reduced vascular resistance. Behavioural practices related to heat loss responses are also influenced by cultural/religious expectations, personal preferences and sociodemographics.

CONCLUSION

The findings from this review suggest that pregnancy modifies evaporative (sweating), dry and behavioural heat loss. However, future studies have an opportunity to compare heat loss measurements accounting for gestational weight gain and thermal sensation/comfort scale to associate physiological responses with perceptual responses across pregnancy.

Management of Restless Legs Syndrome in Pregnancy and Lactation

Restless legs syndrome (RLS) affects about 20% of all pregnant women. RLS symptoms are usually moderate to severe in intensity during pregnancy and can result in insomnia, depression, and other adverse outcomes. Although iron deficiency has been implicated as a potential etiological factor, other mechanisms can also play a role. Nonpharmacologic methods are the primary recommended form of treatment for RLS in pregnancy and lactation. Iron supplementation may be considered when the serum ferritin is low; however, several patients are unable to tolerate iron or have severe symptoms despite oral iron replacement. Here, we describe a case of severe RLS in pregnancy and illustrate the dilemmas in diagnosis and management. We review the literature on the prevalence, diagnosis, course, possible underlying pathophysiologic mechanisms and complications of RLS in pregnancy. We describe current best evidence on the efficacy, and safety of nonpharmacologic therapies, oral and intravenous iron supplementation, as well as other medication treatments for RLS in pregnancy and lactation. We highlight gaps in the literature and provide a practical guide for the clinical management of RLS in pregnancy and during breastfeeding.

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

OBJECTIVES

Despite the well-established benefits of exercise, pregnant women are discouraged from physical activity in hot/humid conditions to avoid hyperthermia (core temperature (T_core) ≥ 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 T_core 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.

Cardiopulmonary exercise testing during pregnancy

The goal of this review is to examine practical considerations when conducting cardiopulmonary exercise testing during pregnancy. In a clinical and research setting, cardiopulmonary exercise testing during pregnancy is valuable in identifying underlying cardiopulmonary conditions, stratifying the risk of adverse pregnancy outcomes, as well as establishing exercise tolerance/limitations. This review encompasses information regarding the unique physiological adaptations that occur throughout gestation (e.g., changes in resting heart rate, blood pressure, glucose, etc.) and how these adaptations impact the interpretation of physiological measurements. There are also key concerns that are unique to pregnant populations that should be considered when participating in exercise (i.e., fetus, ventilation, thermoregulation, urinary incontinence, low back pain, and pelvic girdle pain). This step-by-step review of cardiopulmonary exercise testing outlines pregnancy related adjustments to standardized methods (i.e., screening/documentation, pre- and post-test measurements, protocol specifics, modality selection, and fetal monitoring) which should be considered for the safety of both the participant and fetus. Currently, pregnancy specific exercise testing guidelines are lacking. Therefore, we will be discussing the limitations of current recommendations such as a safe cut off for resting heart rate and pregnancy specific test termination criteria.

Exercise during pregnancy: a comparative review of guidelines

Exercise during pregnancy may be beneficial provided that there are no contraindications. The aim of this study was to summarize and compare recommendations regarding exercise in pregnancy. Thus, a comparative descriptive review was conducted and included guidelines by the American College of Obstetricians and Gynecologists, the Society of Obstetricians and Gynaecologists of Canada and the Royal Australian and New Zealand College of Obstetricians and Gynaecologists. All compared guidelines recommend that pregnant women without contraindications should undertake physical activities regularly, however, the type of workout performed should be adjusted based on the previous exercise experience and the physical condition of each pregnant woman. A variation among the reviewed guidelines was identified on appropriate and inappropriate activities and on indications to interrupt exercise. To summarize, the adoption of an international up-to-date consensus regarding appropriate exercise during pregnancy may be beneficial in ensuring the safety of the pregnant women while promoting their physical and mental health.

Spotlight on the fetus: how physical activity during pregnancy influences fetal health: a narrative review

Before and during pregnancy, women often aim to improve their lifestyle so as to provide a healthier environment for their developing child. It remains unresolved, however, as to whether physical activity (PA) during pregnancy poses a possible risk or whether it might even have beneficial effects on the developing child. There is increasing evidence that PA during pregnancy is indeed beneficial to maternal physiological and psychological health and that it is generally not detrimental to the fetal cardiovascular system and neuronal function in the developing child. This also led to international recommendations for PAs during pregnancy. In the current review, we aimed to comprehensively assess the evidence of beneficial and harmful effects of maternal PA, including high-performance sports, on fetal development. The different mental and body-based relaxation techniques presented here are frequently performed during pregnancy. We found a considerable number of studies addressing these issues. In general, neither low key, moderate maternal PA nor relaxation techniques were observed to have a harmful effect on the developing child. However, we identified some forms of PA which could have at least a transient unfavourable effect. Notably, the literature currently available does not provide enough evidence to enable us to make a general conclusive statement on this subject. This is due to the lack of longitudinal studies on the metabolic and cognitive effects of regular PA during pregnancy and the wide diversity of methods used. In particular, the kind of PA investigated in each study differed from study to study.

MRI safety considerations during pregnancy

The use of magnetic resonance imaging (MRI) during pregnancy is on the rise due its ability to provide detailed cross-sectional anatomy without ionizing radiation. Despite the favorable radiation profile, theoretically concerns regarding the safety of MRI and gadolinium-based contrast agent (GBCA) administration have been raised. Currently there are no studies that have shown any attributable harms of MRI during any trimester of pregnancy although prospective and longitudinal studies are lacking. GBCA administration may be associated with a slightly higher rate of neonatal death, although this is based on a single, large cohort study. Understanding the available evidence regarding MRI safety during pregnancy in the context of current society guidelines will help the radiologist serve as a valuable resource to patients and referring providers.

Current Resources for Evidence-Based Practice, March 2020

An extensive review of new resources to support the provision of evidence-based care for women and infants. The current column includes a discussion of the concept of overdiagnosis and implications for research and commentaries on reviews focused on exogenous progestogen to maintain pregnancies and cancer risk among children conceived using fertility treatments.

Responses of intestinal morphology and function in offspring to heat stress in primiparous sows during late gestation

Late gestation is a key period for intestinal development. Maternal heat exposure may induce intestinal dysfunction of offspring. To investigate the responses of intestinal morphology and function of offspring to the maternal heat stress (HS), twelve first-parity Landrace × Large White sows were assigned to thermoneutral (TN) (18-22 °C; n = 6) or HS (28-32 °C; n = 6) treatment groups at 85 d of gestation until natural farrowing. Twenty-four newborn piglets (two piglets at medium body weight from each litter) were randomly selected and divided into in utero thermoneutral (IUTN, n = 12) and heat-stressed (IUHS, n = 12) groups according to the sow's treatment. Blood and intestinal samples were harvested to evaluate stress hormone levels, intestinal morphology, integrity and barrier function in the newborn piglets. Our results showed that maternal HS piglets exhibited increased serum adrenocorticotropic hormone (ACTH) concentration compared with that observed in the IUTN group. IUHS piglets showed lower lactase activities in the jejunum and ileum, whereas no significant differences were found between the two groups in the length of intestine, villus length or crypt depth. Serum diamine oxidase (DAO) activity was increased in IUHS piglets. IUHS piglets also exhibited decreased ZO-1, ZO-2 and MUC2 mRNA expression in the jejunum, while the protein levels were not affected. Additionally, IUHS piglets had a lower apoptotic percentage and FAS mRNA expression in the jejunum than those in the IUTN group. Taken together, these results demonstrate that high ambient temperature during late gestation of primiparous sows causes stress response in neonatal piglets, compromising intestinal permeability and mucosal barrier function, which may be partly mediated by inducing intestinal apoptosis.

Neurophysiological and cognitive changes in pregnancy

The hormonal fluctuations in pregnancy drive a wide range of adaptive changes in the maternal brain. These range from specific neurophysiological changes in the patterns of activity of individual neuronal populations, through to complete modification of circuit characteristics leading to fundamental changes in behavior. From a neurologic perspective, the key hormone changes are those of the sex steroids, estradiol and progesterone, secreted first from the ovary and then from the placenta, the adrenal glucocorticoid cortisol, as well as the anterior pituitary peptide hormone prolactin and its pregnancy-specific homolog placental lactogen. All of these hormones are markedly elevated during pregnancy and cross the blood-brain barrier to exert actions on neuronal populations through receptors expressed in specific regions. Many of the hormone-induced changes are in autonomic or homeostatic systems. For example, patterns of oxytocin and prolactin secretion are dramatically altered to support novel physiological functions. Appetite is increased and feedback responses to metabolic hormones such as leptin and insulin are suppressed to promote a positive energy balance. Fundamental physiological systems such as glucose homeostasis and thermoregulation are modified to optimize conditions for fetal development. In addition to these largely autonomic changes, there are also changes in mood, behavior, and higher processes such as cognition. This chapter summarizes the hormonal changes associated with pregnancy and reviews how these changes impact on brain function, drawing on examples from animal research, as well as available information about human pregnancy.

PHYSIOLOGY SYMPOSIUM: Postnatal consequences of in utero heat stress in pigs

Postnatal heat stress negatively impacts pig productivity and well-being as animals attempt to manage the resultant strain response. This is especially true when postnatal heat stress is combined with production stressors (e.g., mixing, weaning, transport, handling, and isolation) that have the potential to increase disease occurrence, morbidity and mortality. While pigs can utilize adaptive physiological mechanisms to compensate, these are often unfavorable to efficient livestock production. Specifically, postnatal heat stress decreases weight gain, reduces growth and production efficiency, alters carcass composition, and increases morbidity and mortality. Consequently, decreased animal performance constrains profitability and affects economic sustainability. In addition to the negative effects of postnatal heat stress, prenatal heat stress has long-term consequences that may compromise future piglet well-being and performance. Pigs gestated under heat stress conditions have an increased postnatal stress response and an increase in maintenance energy requirements. Furthermore, prenatal heat stress decreases swine birth weight, and increases teratogenicity, core body temperature set-point, and alters postnatal body composition (more adipose tissue and less skeletal muscle). Taken together, the effects of heat stress during pre- and postnatal pig development negatively influences productivity and well-being, a scenario that threatens the sustainability of global swine production.

Effects of prenatal exercise on incidence of congenital anomalies and hyperthermia: a systematic review and meta-analysis

OBJECTIVE

To investigate the relationships between exercise and incidence of congenital anomalies and hyperthermia.

DESIGN

Systematic review with random-effects meta-analysis .

DATA SOURCES

Online databases were searched from inception up to 6 January 2017.

STUDY ELIGIBILITY CRITERIA

Studies of all designs were eligible (except case studies and reviews) if they were published in English, Spanish or French, and contained information on population (pregnant women without contraindication to exercise), intervention (subjective or objective measures of frequency, intensity, duration, volume or type of exercise, alone ["exercise-only"] or in combination with other intervention components [e.g., dietary; "exercise + co-intervention"]), comparator (no exercise or different frequency, intensity, duration, volume or type of exercise) and outcome (maternal temperature and fetal anomalies).

RESULTS

This systematic review and meta-analysis included 'very low' quality evidence from 14 studies (n=78 735) reporting on prenatal exercise and the odds of congenital anomalies, and 'very low' to 'low' quality evidence from 15 studies (n=447) reporting on maternal temperature response to prenatal exercise. Prenatal exercise did not increase the odds of congenital anomalies (OR 1.23, 95% CI 0.77 to 1.95, I²=0%). A small but significant increase in maternal temperature was observed from pre-exercise to both during and immediately after exercise (during: 0.26°C, 95% CI 0.12 to 0.40, I²=70%; following: 0.24°C, 95% CI 0.17 to 0.31, I²=47%).

SUMMARY/CONCLUSIONS

These data suggest that moderate-to-vigorous prenatal exercise does not induce hyperthermia or increase the odds of congenital anomalies. However, exercise responses were investigated in most studies after 12 weeks' gestation when the risk of de novo congenital anomalies is negligible.