Dates are all estimations and can be off by as much as 2 weeks. The most accurate thing is the sonogram measurements. Did the baby itself measure 6 weeks 5 days or is the date of pregnancy 6 weeks 5 days? There is a difference. Pregnancy is dated by the woman's last menstrual period so two extra weeks are tacked on to baby's age. If that is the case she'd actually be 8 weeks 5 days pregnant whereas baby's actual age is 6 weeks 5 days.
Don't forget that they start counting the pregnancy starting at the date of the last menstrual period, which is about 2 wks before actual conception. So if she was measuring 6 wks 5 days that means that conception would have happened about 4 1/2 weeks prior to that date.
Also, I know several women who knew the exact date of conception because they had iui or ivf, but it was a few days off from the date that the baby was measuring. Babies grow at different rates, and it is very common for a baby to measure a few days ahead, meaning that based on its measurements it looks like it was conceived 4 1/2 wks ago but really it is just a fast grower and it was only conceived 4 wks ago . It sounds like the baby could definitely be yours, but if you aren't sure, the only way to know 100% is a paternity test after it is born.
I worked re due date out to be about 20th oct don't know if I'm right but that would buy the conception more likely towards tue 23/31st January?? What due date did they give
Did you have sex with her before that? my doctor said i got pregnant on the 5th of Oct. my husband was out of town and we had intercourse before he left on the 1st (but sperm can survive for 5 to 7 days). and i stayed with his mother so i wouldnt be at home alone so it would have been impossible for me to see anyone else. if you hadnt had sex with her anytime before the 23rd then i would ask some questions because she got pregnant 2 weeks into January so i would ask