Intercourse 3-4 days before the onset of menstruation usually does not result in pregnancy, and women who have regular periods usually become pregnant when they have intercourse near ovulation. Ovulation can also be calculated for women with regular periods. A woman’s ovulation day is 14 days before her next menstrual period, and 4-5 days before and after the day of ovulation is the easiest time to conceive. 3-4 days before the menstrual period, for women with very regular menstruation, this is no longer a very fertile time, not near ovulation, but relatively speaking a safe time. Therefore, for women with regular menstruation, intercourse 3-4 days before menstruation will not result in pregnancy. However, women’s menstruation is affected by emotional, environmental, spiritual and psychological factors, and also by various factors such as sleeping habits, and may be delayed. Occasional fluctuations in menstruation within seven days of advance or delay are within the normal range, and an occasional delay of about ten days is not considered a disease and does not require treatment. Therefore, if a woman has a delayed period, ovulation will also be delayed, and it is possible to have intercourse and become pregnant 3-4 days before her period. If a woman does not want to get pregnant, having intercourse during non-menstrual period is recommended to take contraceptive measures every time, the method of contraception during the safe period is not strict and easy to fail.