Introduction to Developmental Psychology
Conception, Pregnancy, Birth
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).
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