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www.infertilityspecialistnewyork.com IVF In vitro fertilization is the combination of mature eggs, or oocytes, and sperm in a sterile petri dish. Fertilization occurs when a sperm enters an egg to form a zygote. The in vitro fertilization process begins when the eggs are retrieved from the womans ovaries by a reproductive endocrinologist. The eggs are deposited in a sterile petri dish and taken to the IVF lab. The embryologist examines the eggs under the microscope. This is what he sees. Each dark group of cells is a cumulous-oocyte complex. Here you can see the oocyte at the center. On the oocytes outer membrane, presence of a polar body indicates the egg is mature and ready for fertilization. Outside of the oocyte are the corona radiata cells, surrounded by the cumulus cells and the outermost granulosa cells. Here is the sperm sample, which has been washed to capacitate the sperm. Only these active, capacitated sperm can fertilize an egg. In the standard-culture form of IVF, about 150000 capacitated sperm are added to the petri dish of mature oocytes and allowed to incubate. 16 to 20 hours later, we can see that breakdown of the granulosa cells has occurred. See how dispersed they are? The embryologist removes excess cells so that he can look for pronucleii. Presence of pronucleii in an oocyte indicates that the union of sperm and egg—fertilization–has taken place.