Hiya
When you go for the Scan its actually a dating scan. They are measuring the baby and from these measurements they can predict how far you are gone. However, if your baby is bigger than the average then they are going to put you forward a bit further.
Well this is the impression that I have always got?? Perhaps Im wrong?? When I went they only moved my dates by one day, so I guessed that the Baby was therefore exactly the size that it should have been.
Ive got another scan in 3 weeks (my 20 week scan) I just hope they dont change my dates again!!!
Good Luck with your Pregnancy!
Ragna xxxxxxxxxxxxxxx