Sex 1 day before menstruation will not result in pregnancy, even though ejaculation occurs inside the body. This is because normal pregnancy requires sex during a woman’s ovulation period, which must be after the woman’s eggs have matured and been discharged. And women’s ovulation is, in the next menstrual period before the arrival of about 14 days, in the 3-4 days before and after the day of ovulation, sex is more likely to get pregnant. Therefore, it is relatively safe to have sex within 1 week before the next menstrual period, provided that the woman’s menstrual cycle is regular. And the closer to the time of menstrual bleeding, the safer it is, so ejaculating within a day before the arrival of menstruation will not result in pregnancy. However, the prerequisite is that you usually have a relatively regular menstrual cycle and you can be sure of the arrival time of your next menstrual period. If the usual menstrual cycle is not regular, it will not be possible to accurately determine the time of the arrival of the next menstrual period, and relatively speaking, the ovulation period will not be very accurate.