Well when your OB figures out how far along you are, they calculate from the date of you LMP. So subract about 2 weeks or so from your 12 weeks and that should get you pretty close. I knew the day it happened for me, but I was trying. But you ovulate anywhere from the 8th to the 18th day. Day 1 being the first day of your period. You can also calculate that way. At least down to about the week you got pregnant. Hope this helps!

Lady sicily