Hi, I am 20 weeks pregnant currently. I had unprotected sex with someone other than my husband on 2/15/10. I had a light period that was latert than normal on 2/25/10, then another on 3/25/10. My husband and I had sex on 4/4/10 & 4/8/10, he "pulled out" both times, so I was shocked when I found out I was pregnant in early may. The dr. did an ultrasound on 5/13/10, 6weeks 4days pregnant, due date 1/3/11. Ultrasound 5/27 says 8weeks 4 days. I had another u/s at 17 weeks and it was a few days ahead, due date 12/30/10. Is it possible I could have conceived back in February and the ultrasounds are 6-7weeks off? Or can I be absolutely certain my husband is the father?

You cannot be absolutely certain that your husband is the father of the baby until he passes the DNA test.

In the medical profession we cannot go by dates to determine paternity.

Early ultrasounds are the most accurate as far as dating is concerned.

If your due date is January 3, most likely you conceived on or about April 13-14