Heparin Use During Pregnancy

Information for pregnant women or women who have given birth who are receiving low molecular weight heparin

Heparin is an anticoagulant drug. This means that is slows down blood clotting or “thins” the blood. There are various types of heparin – the type we usually use is a Low Molecular Weight Heparin (LMWH) such as Enoxaparin (also known as Clexane) or Dalteparin.

Venous thrombosis is a condition in which a blood clot (thrombus) forms in a vein (venous thrombosis). Most commonly, venous thrombosis occurs in the “deep veins” in the legs, thighs or pelvis and this is called a deep vein thrombosis or a DVT. A DVT can limit blood flow through the vein, causing swelling and pain, but there is a risk that it can break off and travel through the blood stream. This is called an embolus. If the embolus lodges in the lung this is known as a pulmonary embolus (PE). A PE may cause breathing problems, chest pain and coughing up blood but a large PE can cause collapse and may be life threatening. However, the risk of developing a pulmonary embolus, once a DVT has been diagnosed and treated, is extremely small.

During pregnancy and the immediate period after birth, the risk of venous thrombosis is increased. Your risk of developing a thrombosis will be assessed in pregnancy and after the birth of your baby.

The three most common reasons for women starting heparin during pregnancy or after the birth are:

  • A clot arising during this or a previous pregnancy.
  • An increased risk of a clot forming during pregnancy or after birth, e.g. after some caesarean births or if you are immobile for a period of time.
  • Already on long-term anticoagulation, e.g. recurrent thrombosis.

Is Low Molecular Weight Heparin safe for my unborn baby?

For pregnant women and women who have given birth, heparin is the anticoagulant of choice and is recommended by the Royal College of Obstetricians and Gynaecologists. It does not cross the placenta, and therefore is considered to be safe.

Is it safe to breast feed?

There is no evidence that the heparin, including the one that we use (Enoxaparin),  passes into breast milk due to the nature of the drug. If a very small amount passed into breast milk it is broken down by stomach acids therefore any absorption by a breast fed baby is negligible. No adverse effects on any babies have been reported. Therefore it is considered that heparin is safe for you to have whilst you are breastfeeding.

Are there any alternatives?

Warfarin, another anticoagulant taken in tablet form, does cross the placenta and may harm the unborn child (tetrogenic). Aspirin has a weak protective effect but is not recommended by experts to prevent DVT if the woman is at moderate to high risk. DVT Elastic compression stockings have a protective effect against DVT but can be uncomfortable to wear and are not protective against thrombosis anywhere else but the legs.

How will heparin be given to me?

Heparin is broken down by stomach acids and so cannot be taken by mouth. It must be given by injection into the fatty layer of tissue beneath the skins. They type of LMWH we use is generally given once a day but we may give heparin twice a day, particularly during pregnancy.

It is important that the heparin is given at the same time of day (within two hours) and it is recommended that it be given in the morning if the blood tests to monitor it are needed.

Are there any risks?

Side effects of heparin include:

  • Bruising at the injection site.
  • There may be an increased tendency to bleeding.
  • Slightly increased risk of a bruising  (wound haematoma) if having a caesarean birth.
  • Very rarely there may be allergic type reactions at the injection site or in the body generally, increased blood potassium level, an immune reaction called HIT (heparin induced thrombocytopenia) or possibly bone thinning.

Monitoring for these is part of your clinic visit, but the more serious side effects are almost never seen with LMWH use in pregnancy.

When do I start heparin?

It will depend on why you are receiving heparin as to when your injections will start. Some people start early in pregnancy but others may have treatment only after delivery. A management plan for the heparin will be made which should be kept in your obstetric notes and a copy will be kept in your medical notes.

What is needed to give the injections?

The LMWH comes in preloaded syringes. These should be stored out of direct sunlight but do not need to be refrigerated.

You will be shown how to give the injections.

To give the heparin you will need:

  • Alcohol wipes – to clean the skin before the injection.
  • A sharps bin – to dispose of the used needle and syringe.
  • Heparin – this will be prescribed from the clinic but further prescriptions may be provided by your GP.