Women do not typically get pregnant immediately after their period. According to the American Pregnancy Association, in order to get pregnant, a women must ovulate. Ovulation occurs at some point between days 11 and 21 for most women based on a 28- to 32-day menstrual cycle.
When trying to determine the ovulation cycle, women should begin counting from the first day they started menstruating. The American Pregnancy Association advises to also pay attention to other signs of ovulation, such as lower abdomen pain or a change in vaginal discharge.
Sperm can live for up to seven days in a woman's reproductive system; however, most sperm live no more than three days. This means that a woman who is trying to avoid pregnancy should take precautions at least a week prior to ovulation, which means using protection immediately after the period.