Trimesters: break the 9 months into 3 months segments. Gestation is reported as 40 weeks: count as the beginning from the date of the mother"s last menstrual period. Reported as 38 weeks: begin at conception: conception and the germinal period. Germinal period: after conception, the period of very rapid cell division and initial cell differentiation lasting for 2 weeks, when the fertilized egg is implanted in the wall of the uterus. Conception/fertilization: the union of the sperm and the ovum (egg) Women are born with all the ova and they mature 1 per month during reproductive years; about the 10th day after the start of a menstrual period, stimulated by hormones, an ovum enters the final stage of meiosis. If the ovum is not fertilized, it moves down the tube and disintegrates in the uterus and is sloughed off in the next period. Uterus: the structures that contains and nourishes the embryo and fetus.