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[Stockbild] In vitro fertilization. Image 4 of 4. Light micrograph of a human egg (left) injected with a micro-needle (right) containing a single sperm. This method of in vitro fertilization is known as intra-cytoplasmic sperm injection (ICSI). The injected sperm fertilizes the egg. The resulting zygote is cultured until it reaches an early stage of embryonic development. It is then implanted into the uterus, allowing pregnancy to proceed as normal. IVF treatment enables couples with a range of infertility problems to conceive a child. For a sequence showing penetration of the egg during ICSI, see images M802/205-208. (KEYSTONE/SCIENCE PHOTO LIBRARY/MAURO FERMARIELLO) === ===