Great Aunt is menstruation, and the chances of getting pregnant by having sex the day before menstruation are not very high. If the menstrual cycle is very regular, the day before menstruation usually does not ovulate, the probability of pregnancy is very low. Women’s ovarian ovulation will be affected by women’s emotions, psychological factors, the environment, etc. If the menstrual cycle is not regular, women’s ovulation will be advanced or delayed, and there are also a few factors that can lead to accidental ovulation, the day before menstruation there is also a probability of accidental pregnancy. If you have intercourse on the day before your period and your period is delayed, you can use pregnancy tests, blood tests for HCG and other tests to detect pregnancy after your period is delayed.