Blood Clots in the Legs & Lungs (Deep Vein Thrombosis & Pulmonary Embolism)

What is thrombosis and deep venous thrombosis (DVT)?

Thrombosis is a blood clot in a blood vessel which could be an artery or vein. Veins are blood vessels which takes blood towards the heart and lungs. Deep venous thrombosis is a blood clot that develops within a deep vein of the calf, leg or pelvis. DVT usually occurs in only one leg. If the blood clot moves to the lungs then it is called a pulmonary embolus. The incidence of DVT during pregnancy is 1 in 500 to 1 in 2000 women. 1 DVT occurs more commonly after delivery than during pregnancy.
What are the symptoms of DVT?
  • Swollen leg which could be red, hot and tender
  • Swelling in only one of your calves or legs.
DVT is more common on the left leg compared to the right. Swelling of your foot and legs are very common in pregnancy. Read further on this topic – swelling in your arms and legs. If you are concern, see your doctor especially if you the above symptoms.
What are the complications that could occur with DVT?
The blood clot that have developed could break off and travel in your blood stream and lodges in other parts of your body such as your lungs (pulmonary embolus). Pulmonary embolus is rare but could be life threatening.
What are symptoms of pulmonary embolus?
  • Shortness of breath that may occur suddenly
  • Tightness in the chest
  • Chest pain
  • Coughing up blood
  • Fainting or collapsing
Who are at risk of developing DVT?
  • Pregnant women are ten times at risk of developing DVT compared to non-pregnant women. This is due to the physiological changes that occur during pregnancy.
  • Women with underlying thrombophilia disorders (abnormalities with clotting of the blood) where these women tend to have more ‘sticky’ blood i.e their blood clots much more easier compared to the others.
  • Previous history of DVT
  • Overweight.
  • Has severe pre-eclampsia
  • Have been immobile for a long time due to a caesarean section and long travelling (4 hours or more). The risk of developing DVT after a caesarean section is twice higher compared to a vaginal delivery.
  • Smoker
  • Age more than 35 years old
How is DVT diagnosed?
If you have symptoms suggestive of a DVT, your doctor will order an ultrasound of your leg to detect any evidence of blood clots. However, if you have also symptoms of pulmonary embolus other tests such as a CT Scan of your lungs or a VQ (ventilation perfusion) scan.
Would the scans / x-rays be dangerous for my baby?
The CT scan and VQ scan uses radiation (X-rays). Hence, there is a small risk associated with it. However, this risk needs to be balanced against the risk of undiagnosed DVT or pulmonary embolus which could be fatal for you. The risk of your baby developing cancer in childhood following a VQ scan is very rare (1 in 280,000)2. This degree of risk is minimal in comparison with the 15% maternal risk of death if the pulmonary embolism is not diagnosed and treated.
What is the treatment for DVT?
Your doctor will start you on an anti-coagulant to ‘thin out’ your blood called heparin. The most commonly used heparin currently is a low molecular weight heparin (LMWH). This medication is given via injection under the skin. You need this treatment for the entire duration of your pregnancy and 6 weeks post delivery. In addition, your doctor will ask you to wear special stockings (TEDS) which is a graduated elastic compression stocking to help reduce the swelling in your legs. Pain relief will also be given.
What are the benefits of heparin for you in the treatment of DVT?
  • Reduces the risk of pulmonary embolus
  • Reduces the risk of forming another thrombosis
  • Works to dissolve the blood clot and prevents it from getting any bigger
  • Reduces the risk of long term symptoms associated with DVT known as ‘post thrombotic syndrome’.
What are the potential complications of heparin?
  • Bruising at site of injection
  • Allergic reaction. This happens in only 1 -2% of women. Tell you doctor if a rash develops after your injection. You may need to change to a different type of heparin.
  • LMWH is a large molecule. Hence, it does not crosses the placenta and is safe for your baby.
What should I do when labour starts and I am on heparin?
In you think you are in labour. Call your doctor. They may ask you to stop you heparin injections. If you are planned for induction of labour, stop your injections about 24 hours prior to the date. Your doctor will plan and advice you regarding all of this.
What if I am planning to have an elective caesarean section?
You should have your last injection of heparin about 24 hours prior to operation. It will be restarted about 3 hours after your operation.
What happens after delivery?
Again you need to plan this with your doctor.
  • Usually you could continue taking your heparin injections. If you feel uncomfortable about continuing your injections, talk to doctor about changing it to an anti-coagulant which could be taken orally known as warfarin. Both heparin and warfarin is safe to take during breast feeding.
  • You need to discuss carefully the choice of contraception as you should not take hormonal contraception that contains the ‘oestrogen’ hormone as it is associated with increased risk of developing blood clots.
  • Future pregnancies and the possible need to be on heparin as well
  • It is advisable to wear the graduated compression stocking on the affected leg at least for 2 years.
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1. Marik PE, Plante LA. Venous thromboembolic disease and pregnancy. N Eng J Med 2008; 359: 2025
2. Venous thrombosis in pregnancy and after birth. Patient information. Royal College of Obstetricians and Gynaecologist. London: RCOG, Sep 2008.

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