Preventing blood clots in pregnancy

What is Venous Thromboembolism (VTE)?

There are three types of VTE:

Deep Vein Thrombosis (DVT): a DVT is a blood clot that forms in a deep vein, most commonly in your leg or pelvis.

Pulmonary Embolism (PE): if all or part of the DVT breaks free and passes through your blood vessels, it can reach your lungs. This is called a PE.

Cerebral Venous Sinus Thrombosis (CVST): a blood clot that forms in the venous sinuses of the brain. This is an uncommon site of a VTE.

Signs and symptoms of VTE

DVT – Symptoms can include:

• swelling
• redness/discolouration
• warmth
• tenderness/pain of the legs that may be worse when standing or walking. Occasionally, there are no symptoms except pain.

PE – Symptoms can include:

• coughing
• chest pain/tightness (especially when breathing in)
• sudden unexplained breathlessness
• blood-stained phlegm
• feeling very unwell and/or collapsing.

CVST – Symptoms can include:

• headaches
• seizures
• altered consciousness and other neurological symptoms.

Are VTE’s common in pregnancy?

Pregnancy increases your risk of developing a VTE by approximately five times, with the highest risk being just after you have had your baby. This is because the blood thickens at this time and is more likely to form clots. However, VTE is still uncommon in pregnancy or in the first 6 weeks after birth, occurring in only 1-2 in 1000 women (in the absence of other risk factors).

A VTE can occur at any time during your pregnancy including the first three months. It is therefore important to see your midwife early in pregnancy.

Are VTE’s serious?

Yes. ‘DVT’s are serious because they can result in long term complications such as permanently swollen/discoloured legs, varicose veins, and leg ulcers (known as post thrombotic syndrome).

Also part or all the DVT can break off. If this happens it will travel through your blood vessels and can reach your lungs, this is known as a PE. This is potentially life threatening. Prompt treatment saves lives. While dying from a PE is very rare it remains one of the commonest causes of death in pregnancy in the U.K.

Am I at risk of developing a VTE?

You are at increased risk of VTE if you have any of the following.

Before pregnancy if you:

• are over 35 years of age.
• have already had three or more babies.
• have had a previous VTE.
• have a parent or sibling who has had a VTE.
• have a thrombophilia – an inherited blood clotting disorder that increases the risk of VTE’s.
• have a medical condition such as heart disease, lung disease or arthritis – your doctor or midwife will be able to tell you whether any medical condition you have increases your risk of VTE.
• have severe varicose veins that are painful or above the knee with redness/swelling.
• are a wheelchair user.

Lifestyle if you:

• are overweight with a body mass index (BMI) of over 30.
• are a smoker.
• are an intravenous drug user.

During pregnancy if you:

• are admitted to hospital.
• are carrying more than one baby (multiple pregnancy).
• become dehydrated.
• are less mobile during pregnancy due to problems such as vomiting or infection.
• are immobile for long periods of time, for example after an operation or when travelling for longer than 4 hours (by air, car, or train).
• are unwell from fertility treatment (ovarian hyperstimulation syndrome).
• have pre-eclampsia.

After the birth of your baby If you:

• have a very long labour (more than 24 hours).
• have a caesarean section (x5 higher risk of a VTE compared to a normal vaginal delivery).
• lose a lot of blood after you have delivered your baby.
• receive a blood transfusion.

Can I reduce the risk of getting a VTE?

Most VTE’s that occur during or after birth are preventable so you may be able to reduce your risk. You should be risk assessed during your pregnancy and after you have had your baby, your doctor or midwife will ask if you have any of the risk factors detailed above. This helps them to decide if you would benefit from preventative treatment this will depend on which risk factors you have and how many you have.

Your doctor or midwife will discuss your risk factors and explain why they think you would or wouldn’t benefit from preventative treatment.

When will I be risk assessed?

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

During pregnancy:
Your risk assessment is performed at booking and the midwife will re-check your blood clot risk (to make sure that it has not changed) at every visit.
After your baby is born:

You should be risk assessed again after you have given birth.

Can my risk of VTE change?

Yes, it can increase or decrease during your pregnancy. You might only have one or two risk factors at the start of your pregnancy, but you may develop other factors such as severe varicose veins, being unwell, travelling for more than 4 hours and having a complicated birth. If your risk increases, you might then be prescribed preventative medicine in the form of low molecular weight heparin injections.

Your risk can also decrease, for example you might stop smoking or stop using intravenous drugs which may mean you no longer require preventative medicine.

Similarly, your risk may change from a pregnancy to another (for example: if this is your third pregnancy, if your weight has changed, if you stop smoking, etc.

What can I do to reduce my risk of VTE?

You can reduce your risk of VTE by:

• Losing weight before pregnancy if you are overweight.
• Keeping active during your pregnancy and during labour. Get out of bed and move around soon after giving birth, especially after a caesarean section.
• Maintaining a healthy weight.
• Stopping smoking.
• Drinking plenty of fluid to keep hydrated.

What treatment would be offered to me if I am at risk of VTE?

Wearing special stockings:

If you are admitted to hospital, you might be measured and fitted with anti-embolism stockings for your legs. You should be shown how to wear them and told to tell a health professional about any new pain or discomfort in your feet or legs. Stockings should be worn for 24 hours a day and should only be removed for a short time so that you can have a wash and check for any skin problems. These are particularly useful after a planned C-section when heparin injections are not required.

Wearing Inflatable sleeves:

If you are admitted to hospital the doctor/midwife may ask you to wear calf or foot pumps. These are special inflatable sleeves which you wear around your legs or feet while you are in bed or sitting still in a chair. They will inflate automatically and provide pressure at regular intervals, increasing the blood flow in your legs.

Having a preventative medicine called low molecular weight heparin:

This is an anticoagulant (blood thinner). It reduces your chance of developing a blood clot by thinning your blood slightly.

Is low-molecular-weight-heparin safe for me?

• Low-molecular-weight heparin is generally a safe medication. It may sting a little for few seconds when you inject it, which is normal.
• Allergic reactions occur in about one to two women out of every 100. If you notice a rash at the injection site, inform your doctor or midwife immediately.
• Bleeding complications are very uncommon.

Would using low-molecular-weight-heparin affect my antenatal care or birth plan?

• Low molecular weight heparin does not require monitoring or blood tests in pregnancy, except in high-risk cases where you are reviewed in the Obstetric Haematology Clinic and regular blood monitoring is offered to check heparin levels.
• Use of low molecular weight heparin does not affect how you give birth.

Is low-molecular-weight-heparin save for my baby?

Low-molecular-weight heparin does not cross the placenta, so it cannot harm your baby. It is safe to take during pregnancy.

Is it safe to use low-molecular-weight-heparin injections along with aspirin?

If you have been prescribed aspirin, it is safe to take alongside injections of low-molecular-weight heparin, as it does not significantly increase your risk of bleeding.

Is low molecular weight heparin animal derived?

Low molecular weight heparin is pork derived. Unfortunately, there are not any alternatives with the same effectiveness and safety record. It is not uncommon that some women may have concerns or questions in this regard (including Vegetarians and Vegans, Muslim, and Jewish communities) So, please do not hesitate to speak to a doctor if you would like to discuss this further.

How do I use low molecular weight heparin injections?

1. Wash hands thoroughly with soap and water.
2. Choose an appropriate site on the abdomen for injection. It is also safe to inject into the upper, outer area of the thigh or upper area of the arm.
3. Use a different injection site each day.
4. Avoid injecting 5cm (2 in) around the belly button and do not inject near to any bruising or scars. Heparin must not be injected into the muscles.
5. When you are ready to inject remove the grey needle cap from the syringe.
6. Hold the syringe in your writing hand like a pen, with the other hand gently pinch a fold of skin (approximately an inch) between your thumb and index finger.
7. Gently but firmly insert the needle at a 90-degree angle and continue to hold the skin.
8. Push the plunger down slowly to inject the LMWH over 10 – 15 seconds.
9. Keep the plunger pressed down and remove the needle from your skin keeping it at a 90-degree angle and then release the skin fold but keep hold of the plunger.
10. Do not rub or massage the area as this can cause bruising.
11. Push the plunger down further. This will activate the protective needle cover.
12. Put the used syringe into the sharps bin.

Disposal instructions:

The used sharps bin should be closed and locked as directed. Locked sharps bins should be returned to LTHT for disposal.

Side effects:

If you experience any side effects please contact your doctor, pharmacist or midwife. This includes any possible side effects not listed in the patient information leaflet (PILS) which comes with the drug. You can also report side effects directly via the yellow card scheme at:

Are there any tablet alternatives to low molecular weight heparin?

Unfortunately, there are currently no oral alternatives that have the same effectiveness and safety of low molecular weight heparin in pregnancy:

• Warfarin is an oral blood thinner that is known to affect the foetus between weeks 6 – 12 gestation but it can be used at other times during pregnancy in certain high thrombotic risk situations. It can be used safely with breast feeding but is usually reserved for women who need long term treatment.
• Non-vitamin K antagonist oral anticoagulants (such as dabigatran, rivaroxaban and apixaban) are oral blood thinners that are not licensed for use in pregnancy and breastfeeding because there is little known about their safety in these situations.

How long should I take low molecular weight heparin for?

This will vary depending on your baseline and any temporary risk factors that you have:

• may be used to cover a few days (for example: long distance travel or hospitalisation).
• may be used throughout pregnancy or starting at 28 weeks of pregnancy. This is typically decided early in your pregnancy and is reviewed with subsequent antenatal care visits.
• may be needed for a short period (10 days) or up to 6 weeks after birth. This is typically decided after the birth of your baby and while you are in hospital before going home.

Am I still at risk of VTE whilst on low-molecular-weight-heparin?

Yes. low-molecular-weight-heparin significantly reduces your risk of VTE, but it does not bring it down to zero. Therefore, you must still watch for warning symptoms and signs of VTE as described earlier.

When should I stop low molecular weight heparin?

• If you believe you are in labour or if you experience vaginal bleeding, stop taking low molecular weight heparin and contact maternity assessment centre for advice.
• If you are planned for caesarean section or induction of labour, you should stop using low molecular weight heparin for 24 hours before delivery.
• Epidural and spinal anaesthesia should be avoided if you had a recent injection within the last 12 hours.
• If emergency caesarean section is necessary and the last injection was given within 12 hours, it is unsafe to consider spinal anaesthesia and so, general anaesthesia would be the alternative.

What happens after birth?

The midwives will complete another risk assessment after you have given birth. Depending on your risk of developing a VTE you may need to start low molecular weight heparin injections. If you do need low molecular weight injections, you will be told how long you need to take them for.

Try to drink plenty of water and remain as mobile as possible after you have given birth.

If you are at home and develop any signs or symptoms of a clot, contact your GP or your nearest accident and emergency department immediately.

Can I breastfeed while using low-molecular-weight-heparin?

Yes, Low-molecular-weight heparin does not pass to breast milk.

Where can I get more information?

Treatment of venous thrombosis in pregnancy and after birth.

Pregnancy and Baby, Deep vein thrombosis (DVT).

Venous Thromboembolism in Pregnancy