Adult

Anticoagulation in Pregnancy

Pregnancy is a time when the blood is thicker and more likely to develop blood clots. Because of your heart condition you have been told that your blood needs to be thinned during your pregnancy. None of the treatments for anticoagulation are perfect during pregnancy, and the choice of what is the best course of action can be a difficult one. Depending on your particular heart condition we will be able to give you advice regarding which options of anticoagulation regime are suitable for you – for some people one option or another is clearly preferable. In the end the decision about which option you prefer to take is yours.

General Points

  • While anticoagulation protects against blood clots forming it does not guarantee that no clots will form and this remains a risk during the whole of pregnancy
  • Any form of anticoagulation increases the rate of early miscarriage
  • Any form of anticoagulation increases the risk of bleeding in the mother at the time of delivery
  • We sometimes suggest that you take aspirin in addition to the medications detailed below
  • You will need regular hospital visits and regular blood tests (sometimes weekly!) throughout your pregnancy
  • We may plan to induce your labour or plan a caesarean section a little earlier than usual. We will normally put you on low molecular weight heparin for a few days prior to delivering the baby so the warfarin has time to wear off before the baby is born.

IF YOU ARE TAKING WARFARIN AND DISCOVER THAT YOU ARE PREGNANT YOU MUST CONTACT US AS SOON AS YOU HAVE A POSITIVE PREGNANCY TEST

Option 1: Warfarin throughout pregnancy until just before delivery

This option is suitable for you if you have a metal heart valve which carries a high risk of clotting off in pregnancy or another condition in which you have a high risk of blood clots forming. You will need more regular INR blood tests than you have probably needed prior to your pregnancy.

Pros of taking warfarin throughout pregnancy
Taking warfarin throughout your pregnancy offers you the greatest possible protection from developing potentially life threatening blood clots during your pregnancy.

Cons of taking warfarin throughout pregnancy
Warfarin crosses the placenta and passes into the baby. Taking warfarin between 6 – 12 weeks of pregnancy leads to a 4 – 10% risk of an abnormality developing in your baby. These abnormalities include facial deformity, blindness, limb deformity, fits and mental retardation. The risk of an abnormality in your baby is much lower if you take less than 5 mg of warfarin a day (remember your warfarin requirement may go up in pregnancy). If you are still taking warfarin when you go into labour (ie if you go into labour early) there is an increased risk of you having a serious bleeding complication at the time of delivery, and of the baby suffering bleeding into the brain at the time of delivery.

Option 2: Low molecular weight heparin throughout pregnancy

This option is suitable for you if you have a condition which carries only a moderate risk of developing blood clots during pregnancy. Low molecular weight heparin is given by injection under the skin twice a day. Usually the patient gives these injections themselves after some training, but sometimes a family member gives the injections. You will need to have regular blood tests to ensure that the dose of the medication is correct. For most people we should be able to arrange for your local hospital to do these tests, but sometimes you will need to come up to Leeds to have these done.

Pros of taking low molecular weight heparin throughout pregnancy
Low molecular weight heparin does not cross the placenta and therefore does not affect your baby.

Cons of taking low molecular weight heparin throughout pregnancy
If you have a metal heart valve or other condition which puts you at significant risk of developing blood clots low molecular weight heparin does not offer you as much protection against blood clots forming as warfarin does. Remember blood clots forming can be life threatening and lead to other complications such as stroke or loss of limbs. In some patients taking heparin for prolonged periods can lead to thinning of the bones or problems with low platelet counts.

Option 3: Warfarin throughout pregnancy, except for weeks 6 – 12 when low molecular weight heparin is substituted for warfarin

This option may be suitable for those with moderate risk of clots and some patients with metal heart valves in. Low molecular weight heparin is given by injection under the skin twice a day. Usually the patient gives these injections themselves after some training, but sometimes a family member gives the injections. You will need to have regular blood tests to ensure that the dose of the medication is correct. For most people we should be able to arrange for your local hospital to do these tests, but sometimes you will need to come up to Leeds to have these done.

Pros of taking low molecular weight heparin weeks 6 – 12 of pregnancy
This avoids warfarin crossing the placenta at the time when the baby is most sensitive to it, and avoids the baby developing the abnormalities associated with warfarin therapy.

Cons of taking low molecular weight heparin weeks 6 – 12 of pregnancy
This increases the mothers’ risk of developing potentially life threatening blood clots during the period in which she takes the low molecular weight heparin instead of warfarin.

To do this properly it is vital that you take a pregnancy test as soon as you think you might be pregnant. At this point you will already be 4 weeks pregnant and we must get you off warfarin before you are 6 weeks pregnant – this only gives us all 2 weeks and this can be a busy time! You must let us know as soon as you have a positive pregnancy test.

Adult Congenital Heart Team
Leeds General Infirmary
November 2015