Some women are concerned when the fetus measures size-wize different on ultrasound when compared to their expected due date.It is normal to be within a certain range of an expected measurement at any part of the pregnancy. Not all of us are the same height (!), and the same applies for the fetus. Normal measurements follow a so-called bell-curve.
Up to about the 12th week of pregnancy, a normal range of 7-10 days can be expected, more so later on in pregnancy. For example, after 32 weeks or so, it's normal for the fetus to measure 2-3 weeeks more or less than expected. At 9 weeks, diabetes should not be the reason for the baby measuring slightly bigger, while much later on in pregnancy (after 24 weeks usually), any mother with a baby that's considered too big should be checked for diabetes.