Hi. I was wondering how accurate your first ultrasound is during your pregnancy. The reason why is because I am trying to determine the paternity of my daughter. I had sex with my ex on June 12, 2008 and I also had sex with someone in the very early morning hours of June 16, 2008. The first day of my last menstrual period was June 1, 2008. When I went to my first ultrasound, the doctor told me the due date is March 4, 2009. I was 13 weeks at that point. I calculated this to being one day shy of 40 weeks from the date of June 12th. So, I assumed that my ex is the father. Now, I am almost 35 weeks pregnant and they are saying that they are going to go with the date of my last period. Which puts me at March 8, 2009 now. And that would mean she was conceived on June 15th. How accurate is the first ultrasound? Any advice would be greatly appreciated. Thank you.