The first trimester of pregnancy corresponds to which weeks?

The first trimester of pregnancy corresponds to which weeks?

• A. 1-12 weeks
• B. 13-26 weeks
• C. 27-40 weeks
• D. 40-52 weeks

Answer: (A)

The first trimester runs from the start of gestation through the end of week 12. In prenatal care, pregnancy age is counted from the first day of the last menstrual period, so conception occurs about two weeks later, but the time window from week 1 to week 12 is considered the first trimester. This period is when organ development begins (organogenesis) and is a time of high vulnerability to teratogens, making early fetal development especially critical. The second trimester begins at week 13 and ends at week 26, and the third trimester spans week 27 through around week 40.

The first trimester runs from the start of gestation through the end of week 12. In prenatal care, pregnancy age is counted from the first day of the last menstrual period, so conception occurs about two weeks later, but the time window from week 1 to week 12 is considered the first trimester. This period is when organ development begins (organogenesis) and is a time of high vulnerability to teratogens, making early fetal development especially critical. The second trimester begins at week 13 and ends at week 26, and the third trimester spans week 27 through around week 40.