Carbon monoxide poisoning in pregnancy

What is carbon monoxide?

Carbon monoxide (CO) is a colourless, odourless and tasteless gas produced by incompletely burned gas and solid fuels such as coal, coke, barbecue charcoal, and wood.

Inhaled carbon monoxide reduces the amount of oxygen that can be carried in the bloodstream. Exposure to high levels of carbon monoxide can therefore result in illness or death. Serious health effects such as these most commonly occur following exposure to carbon monoxide as a result of faulty heating appliances (gas and solid fuel boilers, fires) or barbecues being used inside homes, caravans, and tents.

What are the symptoms of carbon monoxide poisoning?

Symptoms of exposure to high levels of carbon monoxide include headache, skin flushing, nausea, tiredness, weakness, problems with balance and co-ordination, memory problems, flu-like illness and dizziness. Breathlessness, chest pain, seizures or loss of consciousness suggest carbon monoxide poisoning.

What are the effects of carbon monoxide poisoning in pregnancy?

During pregnancy, exposure to high levels of carbon monoxide can reduce the amount of oxygen reaching the baby in the womb, potentially affecting its growth and development. Carbon monoxide poisoning can lead to suffocation and death of the mother and baby.

Unnecessary exposure to high levels of carbon monoxide should therefore always be avoided. This can be achieved by ensuring all household gas and solid fuel appliances are installed and regularly maintained or serviced by an appropriately qualified professional. This includes having chimneys in households where solid fuel is burned swept regularly, installing household carbon monoxide alarms, never using barbecues in confined/unventilated spaces (including tents or inside) and not leaving cars running in confined spaces such as garages. Warning signs of a problem include a gas fire burning with a yellow flame instead of blue, sooty marks on the covers of gas fires or yellow/brown stains around boilers, stoves or fires. If the appliance is not burning properly, carbon monoxide levels may be increased. In such cases, the appliance should be switched off immediately and investigated by an appropriately qualified professional.

What if I have been exposed to high levels of carbon monoxide during pregnancy?

If you have symptoms that you think may be caused by carbon monoxide exposure you should urgently seek medical attention, either by contacting your midwife or GP, or attending hospital, depending on the severity of your symptoms. Blood tests to measure your carbon monoxide level will be carried out and, if necessary, oxygen will be administered to help clear the carbon monoxide in your blood in order to reduce the risk of carbon monoxide causing harm to you and your baby. Carbon monoxide poisoning at any stage during pregnancy is likely to carry a significant risk of damage to the baby’s brain and other organs. It is therefore important that pregnant women who are exposed are assessed medically and, if necessary, treated as soon as possible. 

This leaflet summarises the scientific studies relating to the effects of carbon monoxide poisoning on a baby in the womb.

Can carbon monoxide poisoning in pregnancy cause my baby to be born with birth defects?

A baby’s body and most internal organs are formed during the first 12 weeks of pregnancy. It is mainly during this time that some medicines are known to cause birth defects.

There are no published studies that have investigated the chance of birth defects in babies whose mothers experienced carbon monoxide poisoning during early pregnancy. Although there are case reports of babies being born with various birth defects following exposure to carbon monoxide in the womb, it is unclear whether these defects were caused by the carbon monoxide exposure or other factors.

Can carbon monoxide poisoning in pregnancy cause miscarriage?

There are no published studies that have investigated the likelihood of having a miscarriage following carbon monoxide poisoning in early pregnancy. There are a handful of case reports of miscarriages that occurred after exposure to carbon monoxide, but it is not possible to analyse the chance of miscarriage occurring after carbon monoxide exposure from this type of data, or to say for certain that carbon monoxide exposure caused the miscarriages.

Can carbon monoxide poisoning in pregnancy cause stillbirth?

A single study found that stillbirth was three times more common in pregnant women with carbon monoxide poisoning than women in the general population. In some of these cases the mother died, leading to the death of the unborn baby, while in others the mother survived. There are also a number of case reports of stillbirth following exposure to high levels of carbon monoxide in pregnancy, in most cases associated with death of the mother. This suggests that the chance of stillbirth is increased in women with severe carbon monoxide poisoning (for example, where the mother loses consciousness).

Can carbon monoxide poisoning in pregnancy cause preterm birth or my baby to be small at birth (low birth weight)?

There are no published studies that have investigated the likelihood of having a preterm birth (<37 weeks) or a baby with a low birth weight (<2,500 g) following carbon monoxide poisoning in pregnancy. There are case reports of babies being born early and with low birth weights (because of their early delivery) to mothers with carbon monoxide poisoning. However, in many cases these deliveries were induced early due to worries about the health of the mother and/or baby. It is currently unclear whether exposure to high levels of carbon monoxide in pregnancy can lead to labour starting early naturally, or may reduce the growth of the baby in the womb.

Can carbon monoxide poisoning in pregnancy cause other problems in the baby/child?

Neonatal death
There are a small number of case reports of babies who died shortly after birth following carbon monoxide poisoning of the mother around the time of delivery. However, because no studies have assessed the chance of this happening, it is unclear how common this is.

Learning or behavioural problems
A baby’s brain continues to develop right up until the end of pregnancy. It is therefore possible that taking certain medicines at any stage of pregnancy could have a lasting effect on a child’s learning or behaviour.

No studies have investigated learning and development in children exposed to high levels of carbon monoxide in the womb. However, carbon monoxide poisoning in adults can lead to brain damage and there are case reports of babies born with brain damage following exposure to carbon monoxide in the womb. The chance of this occurring appears to be higher following severe carbon monoxide poisoning in the mother.

Will my baby need extra monitoring during pregnancy?

As part of their routine antenatal care most women will be offered a scan at around 20 weeks of pregnancy to look for birth defects and to check the baby’s growth.

Women who have been exposed to high levels of carbon monoxide during pregnancy need to be assessed and treated as soon as possible. Additional scans and extra monitoring of the baby’s growth and wellbeing in the womb may be advised depending on the women’s stage of pregnancy and the level of carbon monoxide poisoning or exposure.

Are there any risks to my baby if the father experienced carbon monoxide poisoning?

We would not expect any increased risk to your baby if the father experienced carbon monoxide poisoning before or around the time you became pregnant.

Who can I talk to if I have questions?

If you have any questions regarding the information in this leaflet please discuss them with your health care provider. They can access more detailed medical and scientific information from www.uktis.org.