Prevention of a Blood Clot (Venous Thromboembolism) in Pregnancy – Antenatal and Postpartum Care

What is venous thromboembolism (VTE)?

Thrombosis is where a clot develops within a vessel, an artery or a vein. Venous thrombosis is where a clot develops within a vein. 

Deep Venous Thrombosis (DVT) is where a clot forms within a deep vein, commonly in the leg. A Pulmonary Embolus (PE) is where a blood clot is lodged within one of the vessels in your lungs. Often a PE is the result of a blood clot that has broken off from its original site that then travels to the lungs and becomes lodged which can become life-threatening.

What causes venous thromboembolism?

Venous thromboembolism may be caused by narrow, blocked or damaged blood vessels. This can be due to poor circulation, inactivity or immobility or as the result of infection. 

How common is VTE in pregnancy?

Pregnancy increases your risk of developing VTE as your blood is more prone to developing clots as the result of pregnancy hormones. VTE occurs in 1-2 in 1000 women during pregnancy or in the first six weeks after having your baby.

DVT or PE can occur at any time during your pregnancy therefore it is important to discuss your risk for developing VTE early with your midwife or doctor.

What increases my risk of developing DVT or PE?

Before pregnancy:

If you:

  • Are 35 years of age or older
  • Have had three or more babies
  • Have previously had DVT or PE
  • Have an immediate family member; mother, father, brother or sister has had a DVT or PE
  • Have a thrombophilia (an inherited condition that increases clotting within the blood)
  • Have a certain medical condition(s) such as heart disease, lung disease, inflammatory disease – your doctor or midwife will give you information regarding your risk based on any medical condition you may have
  • Have limited mobility e.g. wheelchair user


If you:

  • Are overweight – BMI >30
  • Are a smoker
  • Use intravenous drugs

During pregnancy

If you:

  • Are admitted to hospital
  • Are carrying more than one baby e.g. twins 
  • Become unwell due to:
    • dehydration from nausea or vomiting in pregnancy
    • fertility treatment e.g. OHSS
    • develop an infection including Coronavirus (Covid-19)
  • Become less mobile due to:
    • hospital admission
    • travel four hours or longer 
  • Have pre-eclampsia

After Birth

If you:

  • Have had a prolonged labour
  • Have had a caesarean section
  • Had a high blood loss 
  • Received a blood transfusion

When is my risk assessed?

If you are planning a pregnancy and think you may have any risk factors for VTE in pregnancy you should discuss this with your GP. Your GP may wish to discuss this further with a Consultant Obstetrician to see if your risk can be reduced prior to pregnancy.

Your midwife or doctor will assess your risk for developing a VTE at the beginning of your pregnancy, during your pregnancy and after the birth of your baby. At any point where your condition changes in pregnancy, such as hospital admission, your risk may be reassessed.

Your risk for VTE may increase or decrease throughout your pregnancy and delivery.

How can I reduce my risk?

You can reduce your risk of getting VTE by

  • Staying as active as you can
  • Keeping hydrated 
  • Maintain a healthy weight prior to and during your pregnancy
  • Stopping smoking

Depending on your risk factors your midwife or doctor may recommend commencing medical treatment to reduce your risk of developing VTE in pregnancy.

If you are already on treatment to prevent VTE prior to pregnancy your doctor may advise changing this medication to one more suitable for use in pregnancy.

What are the symptoms or signs of VTE?

Symptoms of a DVT

  • Pain, swelling or tenderness in one or both legs – usually your calf
  • Increased warmth of the leg
  • Heavy ache in the leg
  • Redness of the skin over the leg

Symptoms of a PE

  • Breathlessness – may be sudden or come on gradually
  • Cough – can cough up blood
  • Chest pain – may be worse on taking a deep breath in
  • Sudden collapse

If you develop any of the symptoms listed above or are concerned about VTE you should contact your midwife or doctor, or for urgent advice contact NHS 111 or dial 999.

What is the treatment for VTE?

Medication to prevent blood clots are known as ‘anticoagulants’. Anticoagulants reduce your body’s ability to form blood clots by keeping the blood thin.

The most common anti-coagulant used in pregnancy is low molecular weight heparin (LMWH). The dose of the medication is dependent on your risk factors and your weight calculated at the beginning of your pregnancy.

LMWH is given by injection under the skin (subcutaneous) once or occasionally twice a day. This injection should be taken at the same time each day. The LMWH recommended by your hospital trust is Tinzaparin.

You and or a family member will be shown how to administer the injection. You will be given the injections ready to use and told how to store and dispose of the injections.

Are there any risks to me or my baby from treatment with LMWH?

Low molecular weight heparin cannot cross the placenta and therefore cannot harm your baby.

Where you inject the LMWH you may get some bruising which usually fades over a few days. 

1 or 2 in every 100 women (1-2%) will have an allergic reaction after injecting. If you become unwell or notice a rash you must inform your doctor so the type of LMWH can be reviewed and changed if needed. 

How long do I have to take the LMWH for?

If you have risk factors for VTE you may be advised to start LMWH. At what point you are required to start medication will depend on your individual risk factors and will be decided by your midwife and doctor. 

Some women may need to commence treatment early in their pregnancy when they book with their midwife while others may be recommended medication later in their pregnancy.

Often women may be advised to take LMWH for a few days to cover a period of increased risk. 

At other times women may be advised to take LMWH throughout their pregnancy or for the latter stages of pregnancy.

It may be recommended that you take LMWH for a few days after you deliver your baby or up to 6 weeks. 

The total duration of your treatment will be discussed with you by your midwife and doctor.

Do I take my LMWH in labour?

If you are in suspected labour do not take your LMWH for that day. 

If you have been booked for planned induction of labour your midwife and doctor will advise you to take your last dose of medication 12 hours before your admission if you are taking a prevention dose. You will need to stop it 24 hours before if you are on a treatment dose due to recent VTE.  Your doctor or midwife will be able to clarify this for you if you are uncertain about which you are taking.

I’m having a Caesarean Section, what do I do with my LMWH?

If you are having an elective (planned) caesarean section your doctor will advise you when to stop taking your LMWH before your delivery. You will normally be advised to stop taking your medication 12 – 24 hours before your delivery. Your medication will usually be restarted 4 hours after you deliver your baby.

If you have an emergency caesarean section and your last LMWH injection was within 12 hours it may be advised that you will need a general anaesthetic.

Can I breastfeed if I am taking LMWH?

Yes, LMWH is safe to take while breastfeeding

What happens after birth?

After birth you will be advised to be as mobile as possible to reduce your risk for developing VTE. It is also advised that you keep well hydrated. You may be advised to wear compression stockings to help reduce your risk further.

Your risk will be reassessed. Some women who did not require treatment during pregnancy may re-advised to start treatment after birth when their risk is reassessed. 

If you were taking LMWH before the birth of your baby it is likely you will be advised to continue this. 

Your doctor may discuss how to manage your risk in future pregnancies and discuss contraception options as some contraception can increase your risk of VTE.

Data Protection

Any personal information is kept confidential.  There may be occasions where your information needs to be shared with other care professionals to ensure you receive the best care possible.

In order to assist us to improve the services available, your information may be used for clinical audit, research, teaching and anonymised for National NHS Reviews and Statistics.  

Further information is available via Gateshead Health NHS Foundation Trust website (Terms and conditions – QE Gateshead) or by contacting the Data Protection Officer by telephone on 0191 445 8418 or by email [email protected].

This leaflet can be made available in other languages and formats upon request