What could be the problem in this situation?

So, Ive got a friend who is 30 weeks pregnant. She was steadily gaining weight and the baby was too until here recently. She had an ultrasound at 26 weeks and the baby was very small for her gestation. Now at 30 weeks, my friend has LOST 5 pounds, and the baby has not gained any weight since the last ultrasound at 26 weeks..I know this is NOT normal..But I do find it really odd, she has one other child that she never had any problems or complications with..Also, No matter how much she eats her and baby are not gaining weight! Worried about her, and so far, they have nothing to tell her at her dr appts. They are giving her yet another ultrasound soon, but thats all they can do as of right now she says. Just curious, anyone else experience this or know of someone who did? Is there a chance they might have to deliver the baby early if she isnt growing?