How do you know if you're 2 weeks pregnant?

You don't know: Nobody in the world knows she is 2 weeks pregnant when she is 2 weeks pregnant. That is because she is conceiving at that time (we count from the beginning of the last menstrual period, so 2 weeks is about when ovulation occurs). A woman can only look back in time after confirming her pregnancy at about 4-5 weeks pregnant, to see what she was doing 2-3 weeks earlier when she was 2 weeks pregnant.