Hi there,
Just saw this and wanted to respond, even if I'm not in the sub-group of women you're looking for. It could be that you haven't received more responses because the situation you describe is not terribly common.
My 4 yo DD has Down Syndrome and was born via emergency c/s at 35 wks. b/c her placenta started failing quickly and dramatically. Very fortunately, my Mommy instincts kicked in, I noticed her decresed movements and became concerned, and we managed to get out her out just in time -- her apgars were 1 and 1. Today she is a healthy, happy, wonderful little girl and my little miracle.
In my four years of posting on a forum specifically for parents of children w/DS (downsyn.com), we have compared birth notes many times and have found that our children mostly tended to be born a few weeks early (36w on average) and quite a few experienced fetal distress during labor. While some were born a bit small for gestational age (a lot of 5 or 6 lbers), many were not. And some were born full-term or after, and quite hardy and hale apart from the DS. In fact, a mom from my DDC here when I was pg w/Sophie also had a baby girl w/DS and went full-term and had a homebirth and baby was over 9 lbs., if I remember correctly. So it can certainly happen, but it doesn't seem to be all that typical.
Hope this helps!

Guin