A normal pregnancy lasts about 40 weeks from conception to the
birth of a baby. This time is roughly divided into 3 periods:
the first trimester, from conception 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. eMedicineHealth Medical
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