I'm so confused! It seems like every website that I look on says something different about when you start 2nd and 3rd trimesters.

One says you start the 2nd trimester at 13 weeks pregnant the other says 12 weeks pregnant.

One says you start the 3rd trimester at 26 weeks pregnant and the other says 27 weeks pregnant.

Anyone have the real skinny on this? Why is it so difficult to figure out!?