A normal pregnancy lasts about 40 weeks from the first day of your last menstrual period to the birth of a baby. This time is roughly divided into 3 periods: the first trimester, from the first day of your last menstrual period to about the 12th week of pregnancy; the second trimester, from about 13 to 27 weeks of pregnancy; and the third trimester, from about 28 weeks of pregnancy until birth.
Each trimester of pregnancy is marked by developmental changes in the fetus.
Primary Medical ReviewerSarah Marshall, MD - Family Medicine
Specialist Medical ReviewerKirtly Jones, MD - Obstetrics and Gynecology
Current as ofJune 4, 2014
WebMD Medical Reference from Healthwise