Pregnancy information for women with metal heart valves

A guide for women with metal heart valves

If you have, or are considering having a metal (mechanical) heart valve replacement there are particular issues surrounding pregnancy which you need to be aware of.

What are the risks of pregnancy with a metal heart valve?

Studies looking at the outcomes of pregnancies between in women with metal heart valves show that around;

1-3% of mothers died during the pregnancy
More than 25% had bleeding complications, usually at the time of delivery
21% of pregnancies ended in miscarriage (12 – 15 % normally)
3% of babies were born with abnormalities

These issues are partly due to the presence of the valve itself, and partly because of the need to take anti-coagulant drugs.

What can happen to the metal valve in pregnancy?

Metal heart valves can develop blood clots on them. Pregnancy is a time when the blood is especially ‘sticky’ and therefore the chances of a blood clot forming on the heart valve are higher during pregnancy than at any other time. If you do develop a blood clot on your metal valve this is very serious and can lead to a stroke or even death, and there would be a significant chance of losing your baby as a result.

The risk of developing a blood clot on a valve depends on certain factors – how old you were when the valve was put in, how many years the valve has been in for, what position the valve is in, and what size the valve is. Your cardiologist will be able to discuss the riskiness of developing clots on your particular valve.

Even before you become pregnant, to help prevent blood clots developing on the valve you must take anticoagulant medication every day. There are a number of different anticoagulant medications which can be taken, but unfortunately none of them are perfect during pregnancy.


Virtually all people with metal heart valves take warfarin every day. Warfarin is definitely the most effective way of preventing blood clots developing on the heart valves during pregnancy, but there are some potential problems with it;

Warfarin crosses the placenta and can harm your baby as it develops. The most risky time is between 6 and 12 weeks of pregnancy. Warfarin can lead to the following problems; limb and facial deformities, blindness, learning disabilities and fits. The risk of warfarin affecting the baby is 4 – 10%. (That means that for every 100 babies born to mothers taking warfarin, 4 – 10 of them will be affected, but 90 – 96 of them will be completely normal). The risk of the baby being affected may be lower if your daily dose of warfarin is 5 mg or less.

Warfarin can also cause problems in later stages of the pregnancy as it crosses the placenta and it will thin the babies blood as well as your own. There is probably an increased risk of bleeding into the babies brain in women who take warfarin in pregnancy particularly at the time of delivery.


Heparin can be used instead of warfarin in certain circumstances. Heparin comes in a number of different forms. It cannot be taken by tablet, and has to be given either by injection under the skin twice a day – (this can be done by yourself or a relative at home), or continuously through a drip – (you would need to be in hospital to have this). Heparin does not cross the placenta, and therefore does not cause harm to the baby, either during its development or at the time of delivery. Its main drawback however is that it is not as effective in stopping blood clots from forming on the heart valves as warfarin is. Remember – blood clots forming on the valve can lead to death or stroke. We can monitor how effective the heparin is at thinning your blood by taking regular blood tests, sometimes as often as twice a week.

Which anti-coagulants should I take?

Unfortunately there is no ‘right or wrong’ answer to this question. There is no ideal drug to take during pregnancy. We usually try to give our patients as much information as possible, and let them come to their own decision about this. Here are some potential options.

1. Warfarin throughout pregnancy

This is definitely the most effective way to prevent blood clots forming on the valve. (However, the risk is probably still up to 4 per 100) It is associated with a 4 – 10% risk of an abnormality forming in your baby. This risk may be lower if you only need to take a small dose of warfarin normally. It is associated with an increased bleeding risk in both you and your baby at the time of delivery.

2. Low molecular weight heparin throughout pregnancy

Low molecular weight heparin is given by injection under the skin twice a day (you perform the injections yourself). There is a significantly higher chance that you will develop a blood clot on the valve (estimated risk of between 1 in 10 and 1 in 4). Bleeding at the time of delivery is likely to be easier to control. The baby will not suffer the effects of warfarin therapy.

3. Warfarin throughout pregnancy, except for weeks 6 – 12, and around the time of delivery (substituted for low molecular weight heparin)

This regime protects your baby from the effects of warfarin during the crucial early weeks of pregnancy. It also protects your baby from harm due to anticoagulation at the time of delivery. This does expose you to increased risks of blood clots forming during those weeks when you are on low molecular weight heparin rather than warfarin.

Talk to us!

If you have a metal heart valve in and are thinking about trying to become pregnant, please discuss it with us first. We can talk through the various options and help you come to a decision which is right for you.

Adult Congenital Heart Team
Leeds General Infirmary