Define the first trimester.

Define the first trimester.

• A. Weeks 13-27 of pregnancy
• B. Weeks 28-40 of pregnancy
• C. Weeks 1-12 of pregnancy
• D. Weeks 40-60 of pregnancy

Answer: (C)

The first trimester spans the earliest phase of pregnancy, typically defined as weeks 1 through 12 of pregnancy (gestational age counted from the first day of the last menstrual period). During these weeks, foundations for all major organs form, and rapid development occurs. By the end of this period, the embryo has developed into a recognizable fetus, and early screening often begins. The other timeframes correspond to the second and third trimesters (or extend beyond term), so they do not define the first trimester.

The first trimester spans the earliest phase of pregnancy, typically defined as weeks 1 through 12 of pregnancy (gestational age counted from the first day of the last menstrual period). During these weeks, foundations for all major organs form, and rapid development occurs. By the end of this period, the embryo has developed into a recognizable fetus, and early screening often begins. The other timeframes correspond to the second and third trimesters (or extend beyond term), so they do not define the first trimester.