Speak to your doc, hun. I know many use it while ttc as it also helps bloodflow to reproductive area and aids implantation. Most should stop when pg, unless directed by their doc, like yourself due to your condition, as it thins the blood so can heighten risk for mc- but not for you, obviously!

The amount to take is usually about 78-81mg..also known as a baby aspirin in the US. Tesco's sells one at 78mg for pennies i think.
Have a look at this as well
question about baby aspirin
Hope that helps a bit.
Hugs, Omi xxx