Warfarin has been shown to cause birth defects in the first trimester of pregnancy so must be avoided early in pregnancy. In some women, it may be used later in pregnancy, however alternate anti-clotting medication is usually prescribed during pregnancy, such as heparin injections.

It is important not to become pregnant while taking warfarin, if you wish to become pregnant you should discuss this with your healthcare professional first. There are other options available for you during pregnancy and they will help decide which is the best option for you.

Although warfarin is avoided during pregnancy, it is safe to take while breastfeeding. This is because very little of the medication gets into the breast milk, so it isn't able to affect your baby.

Because warfarin affects the way blood clots it is likely that warfarin will affect your period. It would be normal to expect your period to be a bit heavier than what you were used to before you started taking warfarin. You may also find that your period lasts for a little bit longer than normal.

If you find that your period is a lot heavier than normal, or that it lasts for a lot longer than normal, you should inform your doctor. This may be a sign that your INR is above the target range.