Who is this information for?

This information is about reducing the risk of a venous thrombosis if you are thinking about having a baby, are already pregnant or have just had a baby.

If you need information on the diagnosis and treatment of venous thrombosis during pregnancy or after birth, please see the RCOG patient information Diagnosis and treatment of venous thrombosis in pregnancy and after birth (www.rcog.org.uk/en/patients/patient-leaflets/treatment-of-venous-thrombosis-in- pregnancy-and-after-birth).

What is venous thrombosis?

A thrombosis is a blood clot in a blood vessel (a vein or an artery). Venous thrombosis occurs in a vein. Veins are the blood vessels that take blood back to the heart and lungs whereas arteries take the blood away.

A deep vein thrombosis (DVT) is a blood clot that forms in a deep vein of the leg, calf or pelvis.

How common is it in pregnancy?

Pregnancy increases your risk of a DVT, with the highest risk being just after you have had your baby. However, venous thrombosis is still uncommon in pregnancy or in the first 6 weeks after birth, occurring in only 1–2 in 1000 women.

A DVT can occur at any time during your pregnancy, including the first 3 months, so it is important to see your midwife early in pregnancy.

Why is a DVT serious?

Venous thrombosis can be serious because the blood clot may break off and travel in the bloodstream until it gets lodged in another part of the body, such

as the lung. This is called a pulmonary embolism (PE) and can be life threatening. However, dying from a PE is very rare in women who are pregnant or who have just had a baby.

You should seek help immediately if you experience any of these symptoms. Diagnosing and treating a DVT reduces the risk of developing a PE.

What increases my risk of DVT or PE?

Your risk of venous thrombosis is increased further if any of the following apply to you.

Can I reduce the risk of getting a DVT or PE?

You may be able to reduce your risk, as most DVTs and PEs that occur during pregnancy and after birth are preventable.

Babies born earlier than 37 weeks of pregnancy have an increased risk of problems, particularly with breathing, feeding and infection. The earlier your babies are born, the more likely this is to be the case. They may need to be looked after in a neonatal unit. You will be supported to spend as much time as you can with them and you will be encouraged to breastfeed. For more information, see the RCOG patient information Premature labour (www.rcog.org.uk/en/patients/patient-leaflets/premature-labour).

You will have a risk assessment during pregnancy and after you have had your baby, during which your doctor or midwife will ask whether you have any of the risk factors above. This helps to decide whether you would benefit from preventive treatment. This will depend on which risk factors you have and how many.

Some risk factors, such as previous thrombosis, are significant enough on their own for treatment to be recommended. Other risk factors may not be enough on their own for you to require treatment. Your doctor or midwife will talk with you about your risk factors and explain why treatment may be advised in your case.

If you are diagnosed with a DVT, your doctor will give you treatment to reduce the risk of a PE occurring.

When will my risk be assessed?

Before pregnancy

If you have any of the risk factors listed above and are planning a pregnancy you should talk to your GP or midwife. You may need to see an obstetrician early in pregnancy to discuss starting treatment.

If you have previously had a DVT or PE or have a thrombophilia (see above), your GP can arrange a hospital appointment with a doctor who specialises in thrombosis in pregnancy.

If you are already taking warfarin to treat or prevent venous thrombosis, you may be advised to change to heparin injections because warfarin can be harmful to your unborn baby (see section below). Most women are advised to change before becoming pregnant or as early as possible in pregnancy. For some women, warfarin may be the only option. Talk to your doctor before you become pregnant so that any changes can be planned to keep you and your baby as healthy as possible.

During and after pregnancy

Your midwife should carry out a risk assessment at your first antenatal booking and at around 28 weeks of pregnancy. A risk assessment should also be carried out if your situation changes during your pregnancy and/or if you are admitted to hospital. After your baby is born a further risk assessment should be done.

Can my risk change?

Yes. Your risk can either increase or decrease.

You may start by having one or two risk factors but your risk can increase if you develop other factors, such as becoming unwell, developing severe varicose veins, travelling for over 4 hours or having a complicated birth. In this case, you may be advised to start taking treatment.

Your risk may also decrease, for example if you stop smoking. Treatment may then no longer be necessary.

What does heparin treatment involve?

Heparin is given as an injection under the skin (subcutaneous) at the same time every day (sometimes twice daily). The dose is worked out for you depending on your risk factors and your weight in early pregnancy or before you became pregnant.

You may be on a low-dose or a high-dose regimen. You (or a family member) will be shown how and where in your body to give the injections. You will be provided with the needles and syringes (already made up) and will be given advice on how to store and dispose of these.

What happens after birth?

It is important to be as mobile as possible after you have had your baby and to avoid becoming dehydrated.

A risk assessment will be carried out after the birth of your baby. Even if you weren’t having injections in pregnancy, you may need to start heparin injections for the first time after birth. This will depend on what risk factors you have for a DVT. You may be advised to have heparin for 7–10 days after birth or sometimes for 6 weeks after birth.

If you were on heparin before the baby’s birth, you are likely to be advised to continue this for 6 weeks afterwards.

If you were taking warfarin before pregnancy and have changed to heparin during pregnancy, you can change back to warfarin usually 3 days after birth.

At your postnatal appointment, your doctor should:

• discuss future pregnancies – you may be recommended heparin treatment during and after your next pregnancy but if, for example, you stop smoking or lose weight before your next pregnancy, heparin treatment may not be necessary next time
• discuss your options for contraception – you may be advised not to use any contraception that contains estrogen, such as the ‘combined pill’, as this can also add to your risk of DVT.

Making a choice

Sources and acknowledgements

• This information has been developed by the RCOG Patient Information Committee. It is based on the RCOG Green-top Guideline Reducing the Risk of Thrombosis and Embolism during Pregnancy and the Puerperium (April 2015). The guideline contains a full list of the sources of evidence we have used. You can find it online at: www. rcog.org.uk/en/guidelines-research-services/guidelines/gtg37a.
• This leaflet was reviewed before publication by women attending clinics in Glasgow, Coleraine and Sunderland, and by the RCOG Women’s Network.
• The RCOG produces guidelines as an educational aid to good clinical practice. They present recognised methods and techniques of clinical practice, based on published evidence, for consideration by obstetricians and gynaecologists and other relevant health professionals. This means that RCOG guidelines are unlike protocols or guidelines issued by employers, as they are not intended to be prescriptive directions defining a single course of management.
• A glossary of all medical terms is available on the RCOG website at: www.rcog.org.uk/en/patients/medical-terms.