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Reducing the risk of venous thromboembolism (VTE) in pregnancy and the postnatal period

Patient information A-Z

This leaflet is about reducing the risk of blood clots during the pregnancy and postnatal period. This condition is known as ‘venous thromboembolism’ or ‘VTE’.

Treatment may differ but we aim to treat everyone as individuals, respecting your personal wishes and preferences.

What is venous thromboembolism (VTE)?

Deep vein thrombosis (DVT) and pulmonary embolism (PE) together are known as VTE. DVT and PE are two major causes of maternal death in the UK.

Whenever we cut ourselves, our blood hardens and a clot forms. This process is called blood clotting or coagulation. Sometimes a clot of blood can occur within a vein, forming a ‘plug’ that can interrupt the normal flow of blood through the blood vessels. A DVT is a blood clot in one of the deep veins, usually in the vein that runs through the muscles of the calf and thigh.

PE occurs if a clot from a deep vein (usually in the leg) detaches itself and travels to the lungs. Sudden death will occur if the clot is large enough to stop blood flow through the heart and lungs.

VTE is a serious condition which may cause severe pain, swelling, skin changes, shortness of breath and sudden collapse.

Who is at risk?

Anyone can develop a blood clot. However, the risk is higher during pregnancy, and the postnatal period. This is due to an increase in blood volume, an increase in clotting factors in the blood, the effect of pregnancy hormones and the weight of a heavy uterus on the veins that drain the blood out the legs.

Other risk factors include:

  • Smoking
  • Medical history of conditions such as lupus (SLE), heart disease or type 1 diabetes
  • Current IV drug use
  • Age 35 or more
  • BMI of 30kg/m2 or higher
  • Large varicose veins
  • Immobility e.g. wheelchair user
  • Previous blood clot
  • Three or more babies
  • Assisted conception
  • Multiple pregnancy (twins, triplets or more)
  • Hospital admission of more than 14 hours during the pregnancy
  • Hospital admission of more than 3 days postnatally
  • Unplanned caesarean section
  • Blood loss or 1 litre of more
  • Family history of thrombophilia

We use a scoring system, developed by the Royal College of Obstetricians and Gynaecologists (RCOG), to score the risk of clots in pregnancy and determine the need for dalteparin (a low molecular weight heparin [LMWH]).

Why are we assessing you?

It is a recommendation from the National Institute of Clinical Excellence (NICE) and RCOG that all pregnant people have a risk assessment performed in early pregnancy to establish their risk of developing a DVT or PE. This is because prevention of a DVT is crucial in reducing deaths from PE in pregnancy.

Antenatal assessment at booking

This assessment will be carried out in early pregnancy at your first booking visit and is based on a scoring system developed by RCOG. If your score is 3 or more, you will require thromboprophylaxis - a preventative medicine with an anticoagulant (anti-clotting) medicine called a low-molecular weight heparin e.g. dalteparin (Fragmin®). This is administered by a small injection in to your abdomen (tummy).

If your score is 3, we will recommend you start taking this medicine from 28 weeks of pregnancy until delivery. If your score is more than 3, this will be from when you book the pregnancy. You will need some blood test to check your blood count and kidney function before starting the medication. This will be organised via your midwife with your booking bloods. If you live in the Cambridgeshire area your GP will be informed and will issue and continue your prescription throughout pregnancy. If you have a high risk factor, live outside of the Cambridgeshire area or may not be suitable to take dalteparin, you will be referred for an appointment at the obstetric haematology clinic to discuss your care with a specialist doctor.

Antenatal assessment during any inpatient admission

If you need to be admitted to hospital during your pregnancy a further VTE assessment will be carried out by a midwife and if necessary dalteparin will be prescribed for you on the ward by a doctor.

Will being on dalteparin affect how I will give birth?

Taking prophylactic dalteparin during pregnancy should make no difference as to how you birth your baby.

Can I have an epidural or spinal anaesthetic whilst taking prophylactic dalteparin (Fragmin®)?

There must be a 12 hour gap between the last dose of prophylactic (preventative) dalteparin and either a spinal or epidural anaesthetic to minimise any bleeding risk. This errs on the side of extreme caution and follows both national and international recommendations. In practice, more than 95% of those who request one, or who for other reasons need an epidural, can safely have one.

Once labour starts you should stop dalteparin. If you are due a planned caesarean birth, or induction of labour, the last dose will be the day before admission (latest 20:00 that day).

For individuals on treatment doses (higher doses) of dalteparin there must be a gap of 24 hours between the last dose and a spinal or epidural anaesthetic; those on this are seen to offer an individual care plan for birth.

Postnatal assessment

You will be assessed again postnatally for your risk of VTE after birth. Following assessment, if required, you will be given leg stockings to wear and VTE prophylaxis (e.g. dalteparin) will be started and continued for 10 days (or longer if required for some people.)

While in hospital the midwife (or nurse) will give you the dalteparin by injection into your abdomen.

When you are discharged home you will need to continue to use dalteparin and administer it to yourself (or a partner, friend or family member)

How to give yourself an injection of dalteparin (Fragmin®)

You will be shown how to inject yourself with dalteparin by your midwife/practice nurse.

Dalteparin should be kept in a cool, dry and safe place (not a fridge) out of the reach of children. You will be supplied with a sharps box which is a special yellow plastic box to put the used needles in.

How safe is dalteparin (Fragmin®)

Dalteparin is considered safe to use during pregnancy. It does not cross the placenta so your baby is ‘isolated’ from the medicine. Older types of heparin that we no longer use in pregnancy had significant side-effects associated with them but dalteparin does not. The medicine might sting a little when you inject it but this only lasts a few seconds. Some bruising around the injection site is common and can be minimised by pressing on the injection site for three-four minutes after you inject.

Very occasionally a skin rash may appear around the injection site. Often by changing you to a different but similar heparin this disappears.

After you have administered the final dose of dalteparin (Fragmin®)

When you have administered the final dose of dalteparin, lock the sharps box by closing the lid tightly. The box can then be taken to your GP for safe disposal or your community midwife may be able to take it for you.

Other recommended treatments

  • Wear anticoagulation compression stockings, also known as TEDS (thrombo-embolic deterrent stockings). These are made of elastic fibres that squeeze the legs and promote healthy blood flow.
  • Drink plenty of fluids. You should drink enough that your urine (pee) is pale in colour.
  • Stop, or reduce smoking. Your midwife can signpost you to support services.
  • Keep active, and aim to eat a nutritionally balanced diet

Dalteparin (Fragmin®) and breastfeeding

Dalteparin (Fragmin®) does not cross the placenta and a published review of the evidence suggests that these agents are safe for the fetus. Dalteparin is considered safe to use during breastfeeding as it is not secreted in the breast milk.

The RCOG and other sources indicate that the use of the medicine during pregnancy is safe and therefore we are able to endorse the use of dalteparin whilst breastfeeding.

Any questions?

If you have any questions regarding the use of dalteparin, your GP or midwife would be happy to answer these for you. If they have any concerns, they can discuss this with a member of the obstetric/obstetric haematology team.


  • Royal College of Obstetricians and Gynaecologists (RCOG).
  • National Institute of Clinical Excellence (NICE).
  • Hospital Guidelines, Policies and Procedures.
  • Bothamely (2002).
  • Lyons and Kocarev (2007).

We are smoke-free

Smoking is not allowed anywhere on the hospital campus. For advice and support in quitting, contact your GP or the free NHS stop smoking helpline on 0800 169 0 169.

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Contact us

Cambridge University Hospitals
NHS Foundation Trust
Hills Road, Cambridge

Telephone +44 (0)1223 245151