It is unlikely for a woman to get pregnant seven days before her period. On average, a woman ovulates about 12 to 16 days before her next menstrual period, which is when she is most likely to become pregnant.Many health professionals assume women ovulate about 14 days into their menstrual cycles; however, this is not true for all women. An individual woman's time of ovulation often changes from month to month. An egg is only able to be fertilized for 12 to 24 hours, but sperm lives in the body for three to five days. A woman's most fertile time is said to be five to seven days. If a woman has an irregular cycle, it is sometimes hard to tell exactly when impregnation is able to occur.