Extreme heat presents a major public health threat. Pregnant people are more vulnerable, with evidence showing exposure to extreme heat is associated with increased risks for the baby.
What are the risks?
A systematic review () which included studies from 27 countries showed that for every 1˚C increase in ambient (environmental) temperature, the risk for preterm birth and stillbirth increased by 5%.
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 until the end of their pregnancy.
Pregnant people are thought to be at increased risk of heat stress due to changes in their body’s capacity to regulate temperature.
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 by the baby increases the mother’s core body temperature.
When the ambient environment is hotter than the pregnant woman’s core body temperature (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 labor prematurely.
Heat exposure can also release heat-shock protein (a family of proteins produced by cells secondary to stressful conditions) that can damage placental cells and function. This can contribute to poor fetal nutrition, leading to low birth weight.
Strategy to Beat the Heat
In the meantime, with the threat of hot summer days, simple strategies to beat the heat when pregnant include:
1) Drink enough water – take a water bottle with you when out and about
2) Plan your day – avoid the hottest part, of the day if you can. Take a hat or umbrella with you for shade
3) Stay cool – use fans or air-conditioning if possible, close blinds and curtains, and visit a cooled public environment
4) Dress down – wear lightweight, long-sleeved, light-colored, loose-fitting clothes made from natural fibres, such as cotton or linen
5) Go to sleep on your side – at night and for daytime naps to allow the best blood flow to the baby.
These strategies can be adapted to personal circumstances, and of course, seek medical advice if you feel unwell.
Signs of Heat Exhaustion
Signs of heat exhaustion that can lead to heat stroke 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 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 behavior. Heatstroke is a medical emergency