A woman can become pregnant at any time during ovulation, which may happen a week before her period. While it is not typical for a woman to become pregnant right before menstruation begins, she may not know the timing of her ovulation cycle.
The American Pregnancy Association states that the "14 day myth," or the belief that a woman only ovulates (or releases and egg from an ovary) 14 days after her period, most likely stemmed from either an average of when most women ovulate or from dividing the 28-day cycle in half. Not all women ovulate on the 14th day or have a 28-day cycle. The time of ovulation can be affected by irregular periods, the age of the woman and health issues. Since the male sperm can live for 3-5 days and the egg can be released at any time, it is possible for a woman to become pregnant either right before, sometime during or right after her period.