Fertilization can occur as long as there is an egg waiting for the sperm to fertilize it. An egg can survive for 12-24 hours, but sperm can live up to 5 days or even longer inside the woman's body. This means that, even if there is no egg in the tube when you have intercourse, if it occurs one week before ovulation and the sperm is still alive when the egg is released, the sperm could meet the egg anyway. In other words, the woman could get pregnant as well.
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