I am 12 weeks 2 days today and I was curious as to when everyone considers the second trimester to start. I hear a lot of differences in opinion. Ive heard 12 weeks, 13.3 weeks, or 14 weeks. Based on a 40 week gestation 13.3 would make the most sence, but isnt 12 weeks significant at least development wise? I am confused, anyone have any opinions on this??