So sorry to hear about the loss of your daughter.
My wife didn't have anyone in her family with clotting disorders, but if I were you, I'd bring it up to her perinatologist, and as Kris said, ask him or her to run blood tests on underlying clotting disorders (if you can give them more detail on your wife's sister as information becomes available, that will help). Hopefully, they'll run every test possible to give you peace of mind, and work with you to prevent anything going wrong.
Best of luck with this pregnancy. Having a great perinatologist will help with peace of mind, and hopefully with a successful pregnancy.
DW, Norlisa (35)
essential hypertension diagnosed before pregnancy, successfully treated with atenolol, NO preeclampsia antepartum. (post-partum preeclampsia)
Joseph/Josephine Our Angel in Heaven (9/16/02)
Twins Mary Frances and Samuel (a.k.a. Frankie and Sammy) 38 2/7 weeks, 5/26/03