At 37 weeks when he gave me my papers to carry around with me around bring back to each appointment - or to the hospital if I went into labour in the meantime - I noticed that there were a couple of appointments later on in my pregnancies where I was measuring either a
week behind or a
week ahead of where I was in the pregnancy....and I was never told this was something to be concerned about. Both of my sons were born perfectly healthy.
If you're worried, you should ask about it....