The first day of my last period wasn't 9 weeks 0 days ago, either. I'm just not understanding this.

There were only 2 days I could have conceived (yes, I'm sure) and September 27 was one of them. So how could the U/S tech know the exact day I conceived, but I be 9 weeks along???

Please, bear with me. I think pregnancy is confusing and I'm just trying to get a better understanding.