I would like to know how accurate the ultrasound is for conception date as well as any other possible methods. Using the first day of my girlfriends last period July 2, gives a conception date of July 16, we happened to not use protection that weekend at all, and only a few times since, but always pulling out (which I KNOW is not safe). However yesterday she told me she cheated on me only once and happened to be on July 2. He didnt pull out. So now I'm going to have to go get checked out myself for STD's!!! She is going to the OB thurs though to try and get a more accurate date. I just wanted to find out how much more accurate the ultrasound is over simply going by the last period. PS - What sucks about the whole situation is that we have known she has been pregnant since the beginning of the month, and at the doctor's computer's calculated date of July 16 (using the 1st day of last period method), she assumed it was mine. However, it also said Week 7 on the screen, which her friend Amy said would be July 5, so she breaks the whole story down for me. We have been together about 1.5 yrs and just this past week the news of pregnancy started moving from shock to almost looking forward to it. Till this of course. So can the ultrasound or other methods rule down to at least the exact week of conception at this point? Obviously if its mine, I'm going to try to make it work, and if not, we're done. So this is why I REALLY need some peace of mind, whichever way the results go.