Hey ladies! Just wondering, does 2nd trimester start when your 12 weeks, 1 day, 13 wks, 1 day or 14 wks 1 day? This is so confusing to me. I will be 12 weeks soon and with the 12 weeks I will officially go into my 13th week which will be counted as 12 wks 1day etc.. So when does  the 2nd trimester begin EXACTLY?