Re: Counting Pregnancy weeks
I got my last period on 2/21 as well, but I O'd on CD18 (March 10).
I am technically 4 weeks + 5 days, which means that I am in the fifth week. The fetus age is 3 weeks. (You are 5 weeks + 1 day, fetus 3 weeks assuming you O'd on CD14).
Since most people don't know exactly when they O'd, doctors go back to the last menstral period to start the calculations.
40 weeks from LMP.
38 weeks from conception.
Just figure out how your doctor describes it and use that convention. Most of the books I've seen list both side by side.
Last edited by xinerevelle; 03-29-2006 at 07:05 PM.