Both of my babies measured 2 to 2 1/2 weeks larger than their gestational age. They were born weighing 8 lbs. 10 oz. and 9 lbs. 11 oz. Maybe you just make big babies :)
I was measuring 37 weeks at 34 weeks, he came via csection 3 days before his original due date weighing 9 pds 1:oz, so in my case it ment a big baby. But just being a week off shouldn't really change when your gonna have your little one
At this stage baby will grow at different rates, and it can be up to 2cms off each way, so unless you're measuring weeks ahead, every time, it's more likely baby is in a different position or going through a growth spurt right now, or you could just be having a big baby!