Date: April 2023 , Version 4

Quick read

Warfarin is avoided in pregnancy where possible as it can cause birth defects. However, warfarin may sometimes be recommended in patients with mechanical heart valves.

What is it?

Warfarin acts as a ‘blood thinner’. Medicines that work in this way are called anticoagulants. Warfarin is used to treat blood clots, for example, in people with deep vein thrombosis. It can also be used long-term to prevent blood clots for a variety of different conditions.


What are the benefits of using warfarin in pregnancy?

Warfarin helps to treat blood clots and to prevent further blood clots from forming. Blood clots can be serious. If you have a metal heart valve, warfarin is used to prevent blood clots in the valve which can be life-threatening.


Are there any risks of using warfarin in pregnancy?

Yes. Warfarin use in early pregnancy can affect the baby’s bones, as well as development of the face. There are also possible effects on learning and behaviour in children who were exposed to warfarin in the womb.

Warfarin use in early pregnancy has been linked to an increased chance of miscarriage, and in later pregnancy can increase the risk of bleeding in the baby’s brain.

When taking warfarin, it is important to use reliable contraception to avoid an unplanned pregnancy. Women who are planning to conceive should speak to their specialist about whether they need to change from warfarin to a different anticoagulant.

Please do not stop taking warfarin unless advised to do so by a doctor, as this can be dangerous.


Are there any alternatives to using warfarin in pregnancy?

Yes. Switching to a different anticoagulant (such as low molecular weight heparin) is safer for the baby and may be an option, depending on your circumstances.

If you have a metal heart valve you should seek urgent advice from your specialist or GP within a day or two of a positive pregnancy test. Do not stop taking warfarin whilst waiting to be seen as this could be dangerous.

No treatment

What if I prefer not to take medicines during pregnancy?

If a doctor advises that warfarin or other blood thinning medicines should be continued during pregnancy, this is because it is safer for both mother and baby than stopping treatment.

A medicine will only be prescribed during pregnancy if it is needed.

Your doctor or specialist will be happy to discuss the benefits and risks with you.

Will my baby need extra monitoring?

As part of routine antenatal care, all pregnant women in the UK are offered a detailed scan at around 20 weeks of pregnancy. If warfarin is continued, you may receive more detailed scanning of the baby. As pregnancy progresses, you will have extra scans to monitor your baby’s growth and wellbeing.

Are there any risks to my baby if the father has used warfarin?

We would not expect any increased risk to the baby if the father took warfarin 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.

How can I help to improve drug safety information for pregnant women in the future?

Our online reporting system (MyBump Portal) allows women who are currently pregnant to create a secure record of their pregnancy, collected through a series of questionnaires. You will be asked to enter information about your health, whether or not you take any medicines, your pregnancy outcome and your child's development. You can update your details at any time during pregnancy or afterwards. This information will help us better understand how medicines affect the health of pregnant women and their babies. Please visit the MyBump Portal to register.

General information
Sadly, miscarriage and birth defects can occur in any pregnancy.

Miscarriage occurs in about 1 in every 5 pregnancies, and 1 in every 40 babies are born with a birth defect. This is called the ‘background risk’ and happens whether medication is taken or not.

Most medicines cross the placenta and reach the baby. For many medications this is not a problem. However, some medicines can affect a baby’s growth and development.

If you take regular medication and are planning to conceive, you should discuss whether your medicine is safe to continue with your doctor/health care team before becoming pregnant. If you have an unplanned pregnancy while taking a medicine, you should tell your doctor as soon as possible.

If a new medicine is suggested for you during pregnancy, please make sure that the person prescribing it knows that you are pregnant. If you have any concerns about a medicine, you can check with your doctor, midwife or pharmacist.

Our Bumps information leaflets provide information about the effects of medicines in pregnancy so that you can decide, together with your healthcare provider, what is best for you and your baby.