5 Leiden will definitely make you a high risk pregnancy
. Unfortunately, many women with Factor 5 will miscarry due to clots in the placenta, umbilical cord, etc., HOWEVER, just as many will and do carry normal pregnancies. It may have caused your previous miscarriage, however, at least now you are diagnosed and can be treated.
Treatment will most likely consist of a low dose anticoagulant, Lovenox/Heparin.