I would wait until your 12 wk scan before trying to work out what your correct dates are Sometimes the sonographers can measure wrong at this stage, if they are out by a mm, it can change your dates by days. Genetics dont come into play until the 19 wk scan, up till the 12 wk scan they do crown to rump measurements. With #6 the sonographer put me 10 days behind my LMP dates at my 7 wk scan. At my 12 wk scan, i measured 10 days ahead and back at my LMP dates. The sonographer doing my 12 wk scan asked if i had had my 7 wk scan there, which i hadnt and she said "Good, cos that would have been really embarassing for us", so the other sonographer hadnt measured accurately.