Why is there a discrepancy (sp?) between when the end of the first tri is??

BabyS2008

My OB said that the first trimester ends at 12 weeks, my ticker says that I'm officially in the 2nd trimester, but yet other things I read say that it ends at 13 weeks 3 days. Anyone know why??

babyonthebrain2010

13w3d is just the 1/3 of the way done marker based on a 40 week pregnancy.. but since the vast majority of pregnancies aren't exactly 40 weeks, and the 12 week marker goes by the baby's development.. I'd say you are officially in 2nd tri and can celebrate accordingly, you just might not be 1/3 of the way done yet. hopefully that makes sense!

congrats on 12 weeks either way, tho

BabyS2008

Gotcha!! Makes sense. You'd think I'd be smarter about this since I've been through it already. Nope, not so much!! Thanks!!

babyonthebrain2010

hahaha it's not even a silly question, tho, because it seems everything you read goes back and forth. but my doc said 12 weeks, too, and that was how she explained it to me.   as for when the 3rd tri starts I have no idea, but I guess we'll all cross that bridge when we get to it.

KatieM1106

I have seen the 13 w 3 d one many places, and I am always surprised. If you are just going to divide by 3, why trimesters? Why not semesters? Or quarters? 

I am going with 12 weeks.  

LW2410

My Doc's office gives out a sheet of instructions for each tri. I just got the second tri one b/c I won't be back before I start it. It says that second tri is weeks 13-24.

jillybean800

Yep, I think at 12 you are medically into your 2nd tri (developmentally) and the 13.whatever is when you actually divide the 40 weeks into 3.  Congrats!  Yea 2nd tri!