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As we face the continued effects ofÌý, the frequency and intensity of heatwaves is increasing. We’ve recently learnt 2023 wasÌýÌýon record.

Extreme heat presents a major public health threat. It can beÌýÌýfor people who are socioeconomically disadvantaged, and people who have reduced physiological ability to adapt, such as older adults and those with certain medical conditions.

Pregnant people are also more vulnerable, with evidence showing exposure to extreme heatÌýÌýincreased risks for the baby.

What are the risks?

Globally one stillbirth occursÌýÌý²¹²Ô»åÌýÌýare born preterm (before 37 complete weeks of pregnancy) every year. Complications of preterm birth are the leading cause of death and disability for children aged under five years old.

´¡ÌýÌýwhich included studies from 27 countries showed that for every 1ËšC increase in ambient (environmental) temperature, the risk for preterm birth and stillbirth increased by 5 percent.

The risk of stillbirth and preterm birth attributed to heat is greater in lower- and middle-income countries where women are often employed in agriculture or other manual labour positions, and their work continues untilÌý.

Within high-income countries the riskÌýÌý¾±²ÔÌý.

Recent Australian research has also suggested a mother’s exposure to extreme temperatures mayÌý.

Pregnant people are thought to be at increased risk of heat stress due to changes in their body’s capacity toÌý. These changes include:

• increased body mass and body fat which reduces a pregnant woman’s ability to dissipate heat to the environment

• decreased ratio of surface area to body mass can make sweating less effective

• additional energy produced from the baby increases the mother’s core body temperature.

The effects on the body and baby

When the ambient environment is hotter than the pregnant woman’s core body temperature (that is when the air temperature reaches around 38 degrees or above) blood flow is diverted to the skin to allow sweating. This can decrease blood flow to the placenta, meaning less nutrition and oxygen to the baby.

If dehydration occurs, hormonal changes can include the release of prostaglandin and oxytocin, potentially triggering labour prematurely.

Heat exposure can also release heat-shock protein (a family of proteins produced by cells secondary to stressful conditions) which can damage placental cells and placental function. This can contribute to poor fetal nutrition, leading toÌý.

However, actual thermo-physiological data from pregnant women during heat exposure is sparse. OurÌýÌýshowed no study has assessed thermoregulatory function in pregnant women at temperatures higher than 25ËšC.

Our subsequentÌýÌýwith pregnant women showed their bodies regulate temperature up to 32ËšC as well as non-pregnant women.

5 ways to beat the heat while pregnant

Evidence of the effectiveness of interventions that address acute heat exposure during pregnancy specifically are limited. Air-conditioning is exceptionally protective, however it is unaffordable for many in Australia and globally.

More evidence of the effect of extreme heat on pregnancy outcomes at a population level in both low and high income countries will help us develop ways to protect pregnant people and the community.

In the meantime, with the threat of more very hot summer days, simple strategies toÌýÌýwhen pregnant include:

1) Drink enough waterÌý– take a water bottle with you when out and about

2) Plan your dayÌý– avoid the hottest part of the day if you can. Take a hat or umbrella with you for shade

3) Stay coolÌý– use fans or air-conditioning if possible, close blinds and curtains, visit a cooled public environment

4) Dress downÌý– wear lightweight, long-sleeved, light-coloured, loose-fitting clothes made from natural fibres, such as cotton or linen

5) Go to sleep on your sideÌý– at night and for daytime naps to allow theÌý.

These strategies need to be adapted to personal circumstances, and of course seek medical advice if you feel unwell. Signs of heat exhaustion that can lead toÌýÌýif not treated early include:

• sweating and pale, cool, damp skin
• dizziness and weakness
• a headache
• nausea or vomiting
• a rapid pulse and fast, shallow breathing
• muscle cramps
• fainting
• feeling restless and anxious
• heat rash.

If you have these symptoms, find a cool place to rest, drink cool water or a rehydration drink, remove excess clothing, have a cool shower or bath, or sit for a while with your feet in cool water.

More severe symptoms indicating heatstroke include intense thirst, slurred speech, lack of coordination or confusion, and aggressive or strange behaviour. Heatstroke is a medical emergency, so call triple 0.

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This article was first published on and written by University of Sydney researchers Professor Camille Raynes-Greenow,ÌýProfessor Adrienne Gordon,Ìý²¹²Ô»åÌýProfessor Ollie Jay.