Pregnancy Symptoms

Pregnancy 3 Weeks

Fetal Development

Fertilization occurs when the sperm penetrates the egg and the membranes off the sperm and egg unite. Combined they are now called the "conceptus". As the conceptus moves down the fallopian tube, it undergoes rapid cell division.

By the 4th day after fertilization, around the time the egg reaches the uterus, the conceptus consists of 16-32 cells and is called a "morula" ("a ball of cells"). Cell division continues and 7 days after fertilization, there are approximately 250 cells.

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