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
By the end of the first trimester (about week
12 of pregnancy), the fetus has a recognizable human form.
end of the second trimester (about week 27 of pregnancy), all the vital organs
of the fetus have developed. Also, the mother begins to feel the fetus begin to
move (quickening), usually starting between weeks 16 and 20.
the third trimester (about week 28 until birth), the fetus's size increases and
Sarah Marshall, MD - Family Medicine & Kirtly Jones, MD - Obstetrics and Gynecology