me too, yesterday just went scanning, should be 30w, but my fetus stomach is around 28w+, I'm also a bit worried. I already try to eat more, but not sure why still cannot catch up. maybe should try drink the maternity milk also. hopefully next scan will turn better, but I think sudden changes also not good, as long as baby is growing should be fine. My gynae only said my baby will not be a chubby one.
I guess it's because your still in your early stage of pregnancy. don't worry so much,try to eat as nutritious as possible. I went for my last scan and my baby expected to weight about 3.1kg upon delivery. but it weighs 2.3kg when I deliver. so,it's only a gauge . more importantly to have a positive mind,rest well and eat well
Lany