End of First Trimester - end of 12th week or 13th week?

jengsu2004 · August 2011

I feel like this is a silly question, but I've read in several places different things. Are we finished with the first trimester once we have gotten through the 12th week or when we are finished with the 13th week? I have seen it written in books both ways, and I have heard people say different things. I will begin my 13th week tomorrow, so I don't really know if that will be the beginning of my 2nd trimester or if I still have a week to go.

elizxu · August 2011

My OB told me it's actually the first day of your 14th week. Didn't make sense to me, but since then I have had 2 other people say the same thing.

balihaigirl · August 2011

I thought it was the end of the 13th week.

cheese.fiend · August 2011

People measure it different ways - some 12 weeks, some 13 weeks 3 days, some 14 days. My OB does 13 weeks 3 days.

bwtsn · August 2011

I believe it's 13w3d is the first official day of the second trimester. I have no idea why, but I've read that several places.

dr_pr · August 2011

bwtsn:
I believe it's 13w3d is the first official day of the second trimester. I have no idea why, but I've read that several places.

This. And I thought it was because if you take 40 (the "normal" length of pregnancy) and divide it by 3 you get 13.333333, which is roughly 13 weeks, 3 days (really, 2.1, but who's counting?). I'm such a dork Big Smile

jengsu2004 · August 2011

Ha ha...I'M the dork because I am obsessing over this! LOL! I don't know why it's so important for me to know this, but it's just one of those milestones that I want to get to and say, "I'm in my SECOND TRIMESTER! Woohoo!" Like I said, I'm the dork!