Silly question I know, but every book, website etc I read they say something different. Obviously first tri is up to 12weeks, I'm guessing second tri is 13-26ish? I'm 25+1weeks and my DH said "oh you'll be in the 3rd trimester next week" but does that start from 26weeks, 28,29..!? Why doesn't 40weeks divide equally into 3!?