M., you could practically be reciting my situation. My daughter was born at 38 1/2 weeks at 4lbs 6 oz. I had borderline gestational diabetes which I controlled extreemly well. But for some reason my daughter had IUGR. I was already high risk becuase of a birth defect that my husband has (but my daughter does not) so I had a zillion ultrasounds. Everything was completely fine up until about 32 weeks. After that everything went downhill. She just stopped growing and at 38 1/2 weeks she wasn't moving or responding at my sono appt. I went for an emergency c-section that day after weighing all my options - my ob said after the surgery that my uterus was small, the placenta was small and the baby was small. Other than being small and having low blood sugar after birth she was completely developed and fine. They tested my placenta and couldn't determing what caused her growth restriction - they said there was no abnormal decay or problems with the placenta. I am pregnant with my second child so I will be treated as high risk again -- but I am only 12 weeks now and everything looks good so far (not all that reassuring since my problems didn't start until week 32 last time).
Anyway, to answer your probably bigger question -- what does this mean long term? My daughter is 2 1/2 now. Other than still being small she is completely fine. She has been her entire life been very small - even now she is still only 22 lbs and wears 18 month clothes. For most of her first 2 years she was in the less than 3% range for height, weight and head circ. At her 2 yr appt she was still in the less than 3% for weight and head but had moved to 25% for height! Here pedi isn't concerned becuase she has grown parallel to the normal line. I nursed her for 15 months and at about 9 months they dr was concerned that my breastmilk may not be fatty enough so we added the enfamil gentalease formula to pumped milk to give her more calories. Anyway, she is just small - my pedi seems to think that she is just genetically small and this is not a byproduct of what happened while I was pregnant.
As far as developmentally -- she is fine. She rolled over and crawled early. She was a late walker but I think that was stubborness more than anything. She is very smart. She has been able to say her abc's and count to 20 since she was 2, very verbal, almost potty trained, etc.
So don't worry -- we always said -- our daughter was small but mighty!
I was scared too, especially after delivery when she still wouldn't gain weight. But everything is fine now. I have a happy healthy toddler -- and I bet you will too ;-)