Intercourse 4 days before menstruation is usually not pregnant for women who have regular periods, but women with irregular periods who have sex during this period have the possibility of becoming pregnant. Usually, pregnancy can only occur when the woman’s ovum is released and the man’s sperm achieves sperm-egg union. Ovulation usually occurs about 14 days before the next menstrual period, and the egg usually survives for about 24 hours, so the egg is usually already dead by 4 days before the menstrual period and will not be pregnant. However, it should be noted that some women have irregular menstrual periods and their cycles do not last 28-30 days. If ovulation is delayed this month, arranging sex 4 days before last month’s menstrual period may overlap with this month’s ovulation time and result in pregnancy. Therefore, if there is no plan to prepare for pregnancy, women who have irregular periods should still take protective measures when having sex. If there is a delay in menstruation, a woman can check for pregnancy by using a test paper test or by drawing blood. If using test strips, it is best to use morning urine to increase the accuracy rate. In addition, intrauterine pregnancy can be confirmed if a gestational sac is found in the uterus by ultrasound.