Lovenox (or the generic heparin) is an injection used to thin blood. Many times if a woman has a pregnancy history with pre-e, eclampsia, HELLP, or even miscarriages, the OB will recommend thinners as a prevention from the beginning of subsequent pregnancies until near delivery. It can depend on if you have a diagnosed clotting disorder, but I know plenty of women who have used this treatment for unexplained miscarriages.
Whether it works is debatable. It's hard to do studies on pregnant women for ethical and practical reasons. Most pregnant women object to being guinea pigs. My doctor said if he could clone women, so they'd have the same genetic & environmental factors, and let one woman go with treatment and one go without, the results would be more reliable. But in the absense of having that ability (or wanting to), we suggest blood thinners because we *think* they might work.