Trimester Diagram Pregnancy trimesters including first trimester, second trimester and third trimesters. The first pregnancy stage is between 0 to 12 weeks. The 2nd is from 13 to 28 weeks and the third one is 29 to 40 weeks.Trimester Chart. Pregnancy diagram.Trimester Diagram Diagram - Trimester Diagram Chart - Human anatomy diagrams and charts explained. This anatomy system diagram depicts Trimester Diagram with parts and labels. Best diagram to help learn about health, human body and medicine.