I was not on any medication for my first pregnancy. It ended at 28 weeks with an emergency c-section and my baby only lived for 8 days. He had very low cord blood flow and IUGR. I was found to have the Prothrombin G20210A gene mutation, which, according to my perinatologist, causes an inappropriate tendency to form blood clots.
I am currently on Lovenox and have nearly made it to 31 weeks uneventfully. Baby is only measuring in the 35th percentile or so, but my peri says they don't get concerned until the 10th percentile or less. Also, I am having no cord blood flow problems so far.
My peri has told me basically the same thing Kara posted, which is that there currently isn't a lot of support for using Lovenox to prevent PE, but we know it won't hurt. I have also read that if there is any support for it, it is with patients who had very early onset PE.
Based on my factors (severity and fairly early onset), my peri told me I had a 50-60% chance of recurrence and a 10-20% chance of it being as severe and as early. If you haven't had a consult with a specialist yet, that's probably the best way to be informed about your chances of recurrence and the likelihood that Lovenox would make a difference. Even with all the information you can get your hands on, it's a very tough decision to make.