has anyone else experienced this??

Liz
Baby is under weight and tiny as far as inches go at appointment today. He is only on the 33 percentile.
Midwife said that he could be as early as 37 weeks unless my sisters fluid levels drop before. 
My sisters midwife said her weight and measurements are right on track for this stage and baby could just be a small baby. 
His heartbeat is great and so is everything else, except of course the inches and pounds and possibly coming early. 
Had anyone had anything similar to this? How did it turn out?