A woman is most likely to get pregnant if she has intercourse in the days just before and just after ovulation. Ovulation takes place in the middle of the time between two periods. The chance of getting pregnant is less if she has intercourse just before or just after the period. This is why the days just before and just after the period are called the safe period (also called safe days or infertile days). However, the timing of ovulation can vary a lot, and sperm cells can survive for several days in the woman’s genitals after intercourse. She can never be totally sure she will not get pregnant even if she avoids intercourse in the days around ovulation. Safe periods are not a safe contraceptive method.