Yes, I understand the worry when told that your baby isn't growing as hoped. My daughter consistently measured small, but with the opposite measures- her long bones were measuring ok but her head and abdomen were measuring small. Of course, my husband and I thought "oh, no. She is going to have a small head. What will that mean for her?" When I talked to my physician about it, he also said not to worry about it, since maybe she was going to have long legs. And to be honest, she was quite leggy when she was born. And her arms were really long. She looked like a monkey

I think that it is natural to focus on what we consider to be the negatives, but there is often another way to look at these situations.
On a more serious note, ultrasound measures are not as accurate as we are led to believe. And my physician felt the same way about serial ultrasounds. We were having one every two weeks to watch her growth because any sooner than that would not have been informative. While she measured small, she was growing until 30 weeks. And then at 30 weeks, she hadn't shown any growth via ultrasound and the umbilical flow was decreased and the amniotic fluid was slightly low. It was at this point that she was delivered. She was 8 ounces bigger than the ultrasound (five hours before she was born) had predicted.
While we often talk of IUGR here on the forum, I don't know that I have come across any posts dealing with the fact that there are two different classes of IUGR. And I don't remember where I read this but I will look to find a good review for you: The first, Symmetrical IUGR, is characterized by a baby that is small but proportional, long bones and head are all considered to be the same "amount" small. This type of IUGR is thought to arise because the placenta has been severely effected for the entire pregnancy, basically limping along. The second class of IUGR is called "Asymmetrical IUGR" and is characterized by an overall small baby but where the head is proportionately bigger than the body. The idea is that the placenta was working well enough in the beginning to support growth but at some point started to fail. At that point, the baby's brain hijacked more blood flow and was able to continue developing as needed. And here is why I am telling you this- if I recall correctly, baby's born with Asymmetrical (or head-sparing) IUGR do better than baby's born with Symmetrical IUGR.
I'm sorry that you are having to worry about Baby Emma's growth but I am happy to hear that your physician is being very careful and attentive. And I will keep you and Emma in my thoughts.
Diana, happily married since 2007.
Miscarriage at 10 weeks (June 2009).
DD at 30+0 weeks weighing 2lbs 9oz (October 2010) due to PE and IUGR. Today, a happy and healthy toddler.