According to About.com, having sex on the days before an ovulation is the best way to get pregnant because the female is most fertile during this time. The most fertile time for a female, however, is two to three days before ovulation.
According to the American Pregnancy Association, sperm lives in a woman's body for up to five days after intercourse. This makes it possible for a woman to get pregnant from sex that she had during her period. For this to work, however, the woman has to start ovulating very soon after her period ends, which makes it important for all women to know when they start ovulating.