my baby size

Amani
Dear mommies, 
I am in the end of 35-week of pregnancy.
My baby measures differ from a doctor to another , in my regular doctor's device , the long of the leg bone shows younger of age with two weeks.
But in the others' doctor device which is 4D , shows that he is more than his age with some days.
Is that normal? I am worried.
His head size is going with the weeks and his weight is 3KG. 
Please advise,