EED

When I first found out I was pregnant, my DR. and I discuss my EDD (estimated due date) which was January 17^th, 2013.    Today I had my DR. appointment and we discuss my ultra sound results from June 4; everything is GREAT, NORMAL and growing as it should be... BUT… instead of January 17^th, 2013 Dr. is saying that my EED is now January 21^st, 2013.   I guess he is going by the early ultra sound.