in my family, BIG heads seem to be Common. My two daughters had heads measuring a few weeks biiger than dates. Their dad's family all have big heads and thick skulls. My daughters can headbutt anyone/anything with hardly a whimper! And they were both measuring behind in body measurements, however they were both considered adverage when born and both healthy and no real problems. Fingers crossed the same happens with you.....I am sure ur bub will be fine and a good size!