A woman cannot become pregnant if she does not ovulate, but a woman can become pregnant if she has sex several days before ovulation occurs, notes the American Pregnancy Association. This is because sperm can live inside the body for up to five days.
Both an egg and a sperm is needed for pregnancy to occur. Ovulation can happen sometime between day 11 and day 21 of a 28-day cycle. Once an egg is released, it can only be fertilized for 12 to 24 hours. Since sperm can live for five days inside the body, a woman's fertile window is about five to seven days every month, notes the American Pregnancy Association. A woman has only one opportunity to become pregnant each cycle, but some women may release two eggs during ovulation.