Given that I've haemorrhaged after delivering each of my 4 babies - and generally I am prone to bruising/bleeding. My clotting was tested after DC1 - and described as 'just the right side of having van Willebrands disease' (a v. Mild version of haemophilia).
Apparently it reduces the incidence of pre-eclampsia (which I've never had - but I have had pregnancy hypertension in every pregnancy) - and I am advised to take a daily low dose 12 weeks to 32 weeks.