how long does your first trimester last
Pregnancy is measured in trimesters from the first day of your last menstrual period, totaling 40 weeks. The first trimester of pregnancy is week 1 through week 12, or about 3 months. The second trimester is week 13 to week 27. And the third trimester of pregnancy spans from week 28 to the birth. Your baby will change from week to week. To learn more about how your baby is changing each month and about what tests you might think about having, see the Interactive Tool: From Embryo to Baby in 9 Months.