Hot weather and high body temperature during pregnancy

Are pregnant women and birthing people more at risk in hot weather?

Guidance to avoid heat in pregnancy is based on limited research evidence, as pregnant women and people can adjust their body temperature (Samuels et al, 2022).  

However, there do seem to be risks of extreme heat for both the pregnant woman or person and the baby. These are expected to become more of a problem because of the climate crisis (RCOG, no date; Samuels et al, 2022).

These risks include (RCOG, no date; Samuels et al, 2022):

• Dehydration
• Heat exhaustion
• Heat stroke
• Reduction in flow of blood between placenta and baby, leading to the baby being small for gestational age
• An inflammatory response which may trigger pre-term birth 

How to protect yourself when pregnant  

Ways to protect yourself from the risks of hot weather and high temperature include (British Association of Dermatologists, 2024; NHS, 2022 a; NHS, 2022 b; Samuels et al, 2022):

• Wearing sun protection of SPF 30 or above, with a UVA rating of 5 
• While people with Black or Brown skin tones may not usually need sun protection in the UK, those with increased risk factors (or travelling outside the UK) are advised to follow standard guidance
• Stay in the shade between 11am and 3pm  
• Avoid strenuous activities or exercise
• Wearing light coloured and loose-fitting clothing, and a hat
• Stay hydrated with cool drinks, particularly if active
• Avoid alcohol and caffeine
• Have a cool shower or put cool water on skin or clothes

Keep the home cool by (NHS, 2022 a; NHS, 2022 b):

• Monitoring the room temperature
• Opening windows at night when cooler outside
• Closing windows and curtains in the day if indoors is cooler than outside
• Turning off electric equipment and lights that get hot
• Using an electric fan only if the indoor temperature is below 35 degrees (above this temperature the moving hot air increases dehydration)  

Join an NCT Antenatal course or NCT branch to share ideas with other parents on staying cool in pregnancy and beyond. 

Signs of heat exhaustion and heatstroke

Heat exhaustion is when the body has become too hot and needs to be cooled down. If it cannot be cooled down within 30 minutes, it becomes heat stroke. Heat stroke is a medical emergency and needs urgent medical help (NHS, 2022 a).

Signs of heat exhaustion (NHS, 2022 a) include:

• Tiredness
• Dizziness
• Headache
• Feeling / being sick
• Excessive sweating
• Heat rash or change in skin colour (can be harder to see on Black or Brown skin)
• Cramps in the arms, legs and stomach
• Fast breathing or heartbeat
• High temperature
• Being very thirsty
• Weakness

If someone has heat exhaustion, they should (NHS, 2022 a):

• Go to a cool place
• Take off all unnecessary clothing
• Drink a sports or rehydration drink, or cool water
• Use a sponge or spray with cool water to cool their skin  
• Wrap cold packs in a cloth and put them under the armpits or on the neck 

If the pregnant woman or birthing person is still having signs of heatstroke after 30 mins despite having been moved to a cool place and being cooled and drinking fluids, seek medical attention (NHS, 2022 b).  

Signs of heat stroke include:

• Hot skin that’s not sweating
• A fast heartbeat
• Shortness of breath or fast breathing
• Confusion
• A seizure or fit
• Loss of consciousness 

Signs of dehydration

Dehydration means the body has lost more water than it has taken in. It can happen if overheated after a long time in the sun or having been active in hot weather (NHS, 2022 c).

Symptoms of dehydration include (NHS, 2022 c):

• Feeling thirsty
• Dark yellow, strong-smelling urine (wee)
• Weeing less often
• Feeling dizzy / lightheaded
• Feeling tired

Drinking water or diluted squash can reduce the risk of dehydration in hot weather. Foods with a high-water content, like melon and ice lollies, can also help. Alcohol should be avoided (NHS, 2022 c).  

Swelling

Swelling in the ankles, legs, feet and fingers is common in pregnancy. Swelling that comes on gradually and is worse at the end of the day is not usually harmful (NHS, 2024 a).  

The chance of swelling can be reduced by (NHS, 2024 a):

• Avoiding long periods of standing
• Wearing comfortable shoes and socks
• Avoiding tight straps
• Resting with feet raised up
• Regular gentle walks  
• Foot exercises - flexing, stretching, and rotating the feet  

Hay fever

Hay fever is a common allergy to pollen. It is usually worse between late March and September. Symptoms can last for weeks or months, and include (NHS, 2024 b):

• Sneezing and coughing
• A runny or blocked nose
• Itchy, red or watery eyes
• Itchy throat, mouth, nose and ears
• Headache
• Tiredness

There’s no cure for hay fever, but a pharmacist can suggest safe treatments during pregnancy (NHS, 2024 b).

It can also help to (NHS, 2024 b):

• Avoid cutting or walking on grass
• Keep doors and windows shut as much as possible
• Limit time outside when the pollen count is high
• Shower and change clothes after being outside
• Dry clothes inside rather than outdoors
• Put petroleum jelly around the nostrils to trap pollen
• Use filters in the vacuum and car
• Take medication safe for pregnancy that is recommended by a pharmacist

If hay fever is still severe, speak to a GP (NHS, 2024 b). 

What is melasma?

Melasma [mel-az-ma] is also known as chloasma [clo-az-ma] or ‘pregnancy mask’. It is a common condition where darker brown or greyish patches of colour appear on the skin, particularly on the cheeks, forehead, upper lip, nose and chin. It affects up to half of pregnant women and birthing people (British Association of Dermatologists, 2024).  

It is more common in Black and Brown women and birthing people, and those who tan easily or who have a family history of melasma. It tends to be more noticeable in the summer. Although the appearance of melasma can be upsetting, it is not painful, itchy, or contagious (British Association of Dermatologists, 2024).

Melasma is thought to be due to increased pigment following hormonal changes or exposure to ultraviolet light (British Association of Dermatologists, 2024). Hormonal changes include pregnancy, but also birth control pills and hormone replacement therapy.

Ways of reducing the chance of melasma include (British Association of Dermatologists, 2024):

• Avoiding UV radiation from the sun, sunbeds or phototherapy
• Using sunscreen with SPF 30 or above, and a high UV rating
• Wearing a wide-brimmed hat

Melasma will probably disappear after the baby is born, but may return in a future pregnancy.  

Treatment options such as hydroquinone and retinoid creams can normally be used to improve the appearance of melasma but should be avoided in pregnancy as they can harm the baby (British Association of Dermatologists, 2024).  

Chemical peels, microneedling and laser treatments aren’t available on the NHS and could have risks involved with them. Talk to an NHS doctor if melasma is causing distress (British Association of Dermatologists, 2024).