I am a nurse and i have a few questions reguarding the accuracy of early ultrasound dating. My last period was November 17th, 2011. I had a positive pregnancy test on December 22nd, 2011. I went in for my first ultrasound on January 26st and measured at 9 wks 1 day. Everything seems to be right on track! I have been with my boyfriend since October 20th, 2011, i have never cheated on him but i was with someone in early/ towards the middle of october and he was doubting paternity even though the ultrasound says i conceived around november 23rd. What are the chances that the baby may not be his?? Im now at 23 weeks and had one ultrasound at 16 wks where i measured 16.5 wks and another at 21 wks where i measured 22 wks 1 day. Is all this normal? i feel like i have never doubted him being the father but the more he talks i think is it possible for the ultrasound to be off that much? Any info is appreciated thank you!!