How many days off can an ultrasound taken at 13-14 weeks be when determining gestational age?
I've heard everything from 3 days to 2 weeks!
All I know is that the early ultrasounds are the most accurate. My doctors always wanted to do an ultrasound around 9/10 weeks for dating.
Nothing more specific?
No. We aren't doctors here.
If you are worried about paternity a DNA test is the only one that will tell you for sure if you had sex with more than one person over a short period of time.