All of mine were way under their fundal heights, and all 3 are happy healthy children. Ashton was my smallest born at 5lb 13oz, but he was also 4 weeks early. Dont go too much by the estimated weight with scans. Ashton was measuring at 4lb something at my last scan I had and I went into labour that same afternoon. He was born 40hrs later weighing a good pound and a half heavier.