It is not that uncontrollable sugar levels can lead to preeclampsia, in gestational diabetes, there is something funky going on with the placenta, in preeclampsia there is something funky going on with the placenta, so it isn't uncommon for women to have both, or to later get preeclampsia if they have gestational diabetes, to put it as simply as possible. (I know we have posts that go much more in depth on what happens with the placenta for both, but that's pretty much the very very basics of it because I don't remember the specifics off the top of my head.)
Anyway, in my first pregnancy, we are pretty positive I did not have gestational diabetes (no signs of it at all)- but I delivered at 23 weeks so I never made it to the glucose test. In my second pregnancy, I failed the one hour and opted to skip the three hour and just pretend I had GD, so not really sure if I would have passed the 3 hour or not, but my blood sugars were relatively easily controlled (I could even eat Olive Garden), except for my morning fasting numbers were usually borderline (like 90-95ish). I did not develop preeclampsia but DS was 7lb 4 oz at 36+2 so it's possible I would have gotten preeclampsia if we didn't deliver when we did (we delivered due to my prior incision- not symptoms or anything.)
They did give me steroids for DS and were concerned about them messing with my sugars but my blood sugar stayed pretty stable for the most part anyway.
Me (29) DH (30)
#1-Olivia Caetlyn-9-28-09-9-28-09, 23+2 wks, emergency classic c-section, class I HELLP, IUGR
#2- Lucas Oliver (rainbow baby)- April 2011, 36+2 wks, HELLP and pre-e free! (lovenox and LDA pregnancy)
#3-Matthew, late October 2012...mostly normal, 37 wks, (lovenox and LDA again)
My blog: http://www.butterflies-and-rainbows.blogspot.com/