I have the same issue, with my first i was given 5 differing EDD dates. As i have irregular periods and my EDD couldnt be acuratley determined by charts we went by US dates. My son was supposed to be born originally in mid october. We went by the last possible date they gave me which was early november and the hospital let me go Overdue by that last date. (they were confused with EDD) once i gave birth and they check the placenta they told me bubs was actually quite overdue and i would have been around 44 weeks gestation. meaning my 12 week scan would have been accrate.

This time i was told 12 week scan was more acurate as i had MS and by about 12 weeks (i was 13 weeks 3 days at my scan my date changed from my original 7 week scan.) is when they were most acurate.

From what i've been told all EDD are never acurate, i'm just going by my 12 week scan which is 19th may, my 18 week scan showed 25th May but fundus measurements showed i was 2 weeks ahead of that. so were sticking with 19th may...

i guess the only thing EDD are good for is determining if you are too Overdue. i'd just say sick with the 12 week scan and hopefully you'll be lucky and have bubs earlier.

Good luck