The first trimester of pregnancy completes by

TrimestersIt has become customary to divide pregnancy into three equal epochs of approximately 3 calendar months. Historically, the first trimester extends through completion of 14 weeks, the second through 28 weeks, and the third includes the 29th through 42nd weeks of pregnancy. Thus, there are three periods of 14 weeks each.Reference: William's Obstetrics; 24th edition; Chapter 9; Prenatal care