Best way to think of it is pregnancy from conception really is 38weeks 2 weeks are added as they date you from the first day of your last period. 38 divided roughly by 3 is 12.6 days roughly so in your 13th week you are considered in your second trimester then between 26 and 27 in your 3rd. Everyone works it out differently you just need to ask one person usually your midwife and stick to their guidelines xxx Happy pregnancy x
When I went to the doctor he said 13 weeks was second trimester. I'm now 26 weeks and he said 27 weeks is third trimester. It's honestly confusing. Everyone says different. I heard 12,13,14 and 16 weeks to start second trimester
Trimester refers to three time periods of equal lengths. So, given that a full-term pregnancy is 40 weeks, 40 divided into 3 parts = 13.3 weeks per trimester. You end your first trimester at about 13 weeks and 2 days.