My Max was born at 25 weeks and only weighed 1lb 3ozs and he was 11.5 inches long, he was classified as IUGR (I think stands for In Utero Growth Retardation). Anyways, means very small for gestational age. His weight gain has been a constant struggle for us. He left the hospital just a few days after his due date at 6lbs. 12 ozs and 17 3/4 inches long. Not too bad. But since then he developed a severe milk allergy, which was thought to be reflux, and it took awhile to finally sort it out. He had one really slow month of gain, but now he is gaining about 1/2 ounce/day. He is 11 months and weighs about 15.5 lbs. I still feel like it is really small, but the doctors tell me he is growing at a better rate than other babies his real age, so eventually he should catch up. What you want to see is an upward steady trend. And if your baby is gaining more than the rate of an average 5 month old, that is a great sign. My baby book tells me that 5 month olds gain about 1 1/2 lbs during their fifth month. So as long as he is doing this, or slightly better, I wouldn't worry too much.
Hope this helps! [:)]
Mom to Max, 25 weeker, 1/20/03