This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Gynaecology & Obstetrics
The first trimester of pregnancy completes by 
Select and explain. 
A. 10weeks, B. 12weeks, C. 13weeks, D. 14weeks
D: 14weeks
Answer: D: 14weeks 
Explanation: 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