In vitro fertilization (IVF)

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Blastocyst

Illustration of a blastocyst

Three days after fertilization, a normally developing embryo will contain about six to 10 cells. By the fifth day, the fertilized egg is known as a blastocyst — a rapidly dividing ball of cells. The inner group of cells will become the embryo. The outer group will become the cells that nourish and protect it.
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