Twins birth weight!

Hi, I'm pregnant with my second, actually second and third (boy/girl twins) and I had pre eclampsia with my first pregnancy and she was born 3 weeks early and weighed6lbs 3oz, I am a bit concerned about this pregnancy because I have a higher chance of developing Pre E again and having low birth weight babies.  Not to mention twins tend to come early.  I was wondering if any of you had twin babies already or know anyone who has had them what are the average birth weights?  I have heard 4-5 lbs but then I heard stories of people having 6-7lb twin babies so I am just not sure.  I'm doing everything possible to stay healthy in this pregnancy to help fend of f the Pre R and have normal healthy babies.