In terms of your question though.... You need a paternity test.
Pregnancy is calculated from the first day of your LMP. Almost every female knows the date their last period started, but extremely few know the exact date of ovulation. Since most women also have a 28 day cycle, this gives doctors (and the women) a bit of wiggle room regarding gestational age and an estimated due date.
That's why many women have an ultrasound and are behind or ahead on how far they thought they were, because they ovulated early or late. This is actually also why you shouldn't rush labour - while ultrasound and the like is useful, the real gestation of the baby is a guess and they can easily be outside the guess given.
Which Makes Me 22 Weeks And 4 Day
Hi The Reason Why I Asked Was Because My Last Mentstrual Was Nov 28 2012 I Hadd Sexual Intercourse Around Dec 6 Dec7 With This Guy And Then I Had Sex On Dec 19 With My Ex I Hadd Implantation On Dec 29 And When The Doctor Go By My Lmp My Due Date Is Sept 4 2013 But By My U/s Its Sept 12 2013
Gestational age is from the time you actually conceived the baby, but for some reason (Something about periods) You're always two weeks ahead of that (Being your pregnancy week). Like, I'm 22 weeks by my pregnancy weeks, but gestational age I'm only 20 weeks.