When a woman is 3-4 days after her period and 1 week before her next period, it is a safe period. 3-4 days after menstruation, the follicles are not ovulating and the lining of the uterus is thin, so it is not easy to get pregnant after sex, which is a safe period. One week before the next menstrual period, the luteal phase of the ovaries is atrophied and the eggs are dead after ovulation, so the sperm cannot encounter the surviving eggs after sex and the woman will not get pregnant. During a menstrual cycle, ovulation is the time in between periods, also known as the danger period, during which a woman has a higher chance of becoming pregnant. A woman’s safe period and danger period are relative, and when ovulation occurs early or late, it can also cause a woman to become pregnant during the safe period. Therefore, if you do not want to get pregnant, you should use effective contraception even during the safe period.