When does the second trimester start?

B

I’ve recently been involved in a few *discussions* as to whether the second trimester begins at 13 or 14 weeks. I’ve always thought it was 13 but so many people argue (quite forcefully in fact) that it’s 14 and it’s been debated on quite a few posts recently.

According to Tommy’s (a trusted site who is a certified member of the Information standard) it begins at 13 weeks.

Im hoping this is the case because I’m 13w today and am so desperate to be in trimester two!