With in vitro fertilization, eggs are removed from a woman's ovary and exposed to sperm in a culture chamber. Fertilization usually occurs within a few hours, resulting in a microscopic embryo. The embryo grows in an environmentally controlled chamber for 3 to 5 days, with close observation to ensure that development is normal. Once the embryo reaches a certain size, it is ready for transfer into the uterus. This procedure is done in a doctor's office by inserting the embryo via a thin tube, called a catheter, through the woman's vagina and into her uterus. More than one embryo is often transferred to increase the chances of successful implantation into the uterine lining. Any unused embryos are usually frozen under special conditions to ensure their survival for possible use later.
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