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[Stockbild] In vitro fertilization. Image 3 of 4. Computer artwork of a dividing fertilized egg cell (centre) into which a sperm cell was injected during in vitro fertilization (IVF). The injected sperm cell fertilized the egg cell to form a zygote which has genetic material from the mother and father. The cell then divides several times to form a ball of cells in the first stage of embryonic development. It is then placed in the uterine wall, allowing pregnancy to proceed as normal. IVF treatment enables couples with any of a range of infertility problems to conceive a child. For a sequence showing the development of an embryo from IVF treatment, see images M802/237-240. (KEYSTONE/SCIENCE PHOTO LIBRARY/CHRISTIAN DARKIN) === ===