For a woman to have a chance to conceive, she must ovulate. At ovulation, the fallopian tubes will hover over the ovaries and transport the mature egg into the fallopian tube. If the egg comes into contact with sperms, fertilization can occur and there is a chance the woman can become pregnant.
The egg remains in the tube for a few days but the actual period of time for which it is fertilizable is very short, normally less than 1-2 days. If the egg does not meet any sperms, it will break down in the tube and be naturally resorbed.
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