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Stages of Pregnancy

During a full-term human pregnancy, a fetus is carried in the uterus for a gestation period averaging 280 days from the last menstrual period until birth (266 days from conception to birth). The 280 days are frequently divided into 10 four-week lunar months of 28 days each, which equal slightly more than nine calendar months, as shown in Figure 1 . Pregnancies are also often divided into trimesters, periods of three calendar months (13 weeks).





Figure 1

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