Blood clots (thrombosis) during and after pregnancy

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

In pregnancy and for six weeks afterwards, 2 in every 1,000 women will develop a venous thrombosis. Although uncommon it is still 10 times more likely than if you had not become pregnant. A DVT can occur at any time during your pregnancy, including the first three months, so it is important to see your midwife early in pregnancy.


What happens after birth?Show [+]Hide [-]

It is important to be as mobile as possible after you have had your baby and avoid becoming dehydrated. If you were on heparin before the baby’s birth, you may need to continue this for between one and six weeks afterwards.

Even if you weren’t having injections in pregnancy, you may need to start having injections for the first time after birth.

Can I breastfeed?

Yes. Heparin is safe to take when breastfeeding. Warfarin (another anticoagulant that is occasionally prescribed) is also safe to take when breastfeeding.

What should I do when labour starts?Show [+]Hide [-]

If you think you are going into labour stop your injections, phone the maternity unit and tell them that you are on heparin treatment.

What does heparin treatment involve?Show [+]Hide [-]

A daily Heparin injections work as an anticoagulant to ‘thin the blood’ making clots less likely. Unfortunately Heparin cannot be given as a tablet so you will be shown how and where in your body to give the injections. We provide the needles and prepared syringes and you will be given advice on how to store and dispose of these.

How long will I need to take heparin?

This varies from only a few days, for example to cover long distance travel, or treatment may be recommended for the week immediately after delivery. Sometimes treatment is of benefit for the whole of your pregnancy and for up to six weeks after the birth.

Are there any risks from heparin?

A low-molecular-weight heparin is used which does not cross the placenta so it cannot harm your baby. There may be some bruising where you inject – this will usually fade in a few days. One or two women in every 100 will have an allergic reaction. If you notice a rash after injecting you should inform your doctor so that the type of heparin can be changed.

Can the DVT and pulmonary embolism risks be reduced?Show [+]Hide [-]

Yes, your midwife should carry out a risk assessment score at your first antenatal booking. Written in your personal maternity record this assessment is then updated if your situation changes. A further risk assessment should also be carried out if you are admitted to hospital and will be repeated after you have had your baby.

This assessment score helps to decide whether you would benefit from preventative treatment with Heparin. Your midwife or obstetrician will talk with you about your risk factors and explain why treatment may be advised. Heparin is also used to if you have a venous thrombosis, but the dose of heparin used to prevent a venous thrombosis is usually less.

Following these steps will reduce your risk:

  • Staying as active as you can
  • Wearing special stockings (graduated elastic compression stockings) helps to prevent blood clots
  • Keeping hydrated by drinking normal amounts of fluids
  • Stopping smoking
  • Losing weight before pregnancy if you are overweight.

Why is a DVT serious?Show [+]Hide [-]

Venous thrombosis can be serious because the blood clot may break off and travel in the blood stream until it gets stuck in another part of the body, such as in the lung. A clot in the lung or ‘pulmonary embolism’ (PE) is potentially life threatening. The symptoms of a pulmonary embolus include:

  • Sudden unexplained difficulty in breathing
  • Tightness in the chest or chest pain
  • Coughing up blood
  • Feeling very unwell or collapsing

Seek help immediately if you experience any of these symptoms. Diagnosing and treating a DVT reduces the risk of developing a pulmonary embolus.

Varicose veinsShow [+]Hide [-]

Varicose veins lie under the surface of the skin and are different from the deep veins that may develop clots during pregnancy. It is very unlikely that varicose veins will need any treatment during pregnancy and they do not increase your risk of a DVT.

Occasionally compression stocking may be recommended to give some symptomatic relief. Varicose veins in the leg and groin will often improve in the days and weeks following the birth.

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