Carbon monoxide poisoning in pregnancy

(Date: May 2017. Version: 2)

This factsheet has been written for members of the public by the UK Teratology Information Service (UKTIS). UKTIS is a not-for-profit organisation funded by the UK Health Security Agency (UKHSA) on behalf of UK Health Departments. UKTIS has been providing scientific information to health care providers since 1983 on the effects that medicines, recreational drugs and chemicals may have on the developing baby during 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  

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General information 

Up to 1 out of every 5 pregnancies ends in a miscarriage, and 1 in 40 babies are born with a birth defect. These are referred to as the background population risks.  They describe the chance of these events happening for any pregnancy before taking factors such as the mother’s health during pregnancy, her lifestyle, medicines she takes and the genetic make up of her and the baby’s father into account.

Medicines use in pregnancy

Most medicines used by the mother will cross the placenta and reach the baby. Sometimes this may have beneficial effects for the baby.  There are, however, some medicines that can harm a baby’s normal development.  How a medicine affects a baby may depend on the stage of pregnancy when the medicine is taken. If you are on regular medication you should discuss these effects with your doctor/health care team before becoming pregnant.

If a new medicine is suggested for you during pregnancy, please ensure the doctor or health care professional treating you is aware of your pregnancy.

When deciding whether or not to use a medicine in pregnancy you need to weigh up how the medicine might improve your and/or your unborn baby’s health against any possible problems that the drug may cause. Our bumps leaflets are written to provide you with a summary of what is known about use of a specific medicine in pregnancy so that you can decide together with your health care provider what is best for you and your baby.   

Every pregnancy is unique. The decision to start, stop, continue or change a prescribed medicine before or during pregnancy should be made in consultation with your health care provider. It is very helpful if you can record all your medication taken in pregnancy in your hand held maternity records.

Disclaimer: This information is not intended to replace the individual care and advice of your health care provider. New information is continually becoming available. Whilst every effort will be made to ensure that this information is accurate and up to date at the time of publication, we cannot cover every eventuality and the information providers cannot be held responsible for any adverse outcomes following decisions made on the basis of this information. We strongly advise that printouts should NOT be kept for any length of time, or for “future reference” as they can rapidly become out of date.

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