If you have regular periods, you will not get pregnant if you have intercourse the day before your period. Because ovulation occurs 14 days before menstruation, the egg will die in about 24 hours after ovulation without fertilization. The day before menstruation, the egg will have already died, so even if you have intercourse, it is clinically difficult to get pregnant without contraception. It is recommended that in everyday life, if you are having intercourse during ovulation, it is best to take contraceptive measures. It is recommended that you can use condoms to prevent pregnancy, and use condoms during the whole process of sexual life, so that it will be safe. If you usually have irregular periods, if you have intercourse the day before your period, you will not necessarily have your period the next day, and it will be delayed, which may lead to pregnancy in this case.