Because pregnancy is considered from first day of last period. I know it's weird how it works I felt the same way lol.
For instance my last period was Sep 12th I conceived on sep 26th. So when I found out on the 10 th of Oct I was 4 weeks pregnant not 2 it was hard for me to fathom to :)
Weird because I like accuracy! I want to know my baby's actual size, week, etc.. Thank you, again!
Yeah its weird. They date it as if you was already 2 weeks pregnant.. If that makes sense??