Normally, menstruation is very regular, in theory, the week before menstruation belongs to the safe period, the chances of pregnancy are not great, but in the case of coitus without taking any protective measures, there is still a possibility of pregnancy, not 100% will not get pregnant. Menstruation can be delayed or advanced due to a variety of factors. Sudden exposure to cold, environmental changes, bad moods, stress, taking certain medications, etc., leading to changes in the menstrual cycle. When the menstrual cycle changes, the follicular development cycle will also change accordingly, and the ovulation day will be delayed or advanced, so the safe period of intercourse is not necessarily safe. If you are not planning to get pregnant at this time, it is recommended that you try to take contraceptive measures, such as condoms. If you have already had intercourse and have not used contraception, you can also take remedial measures. Go to the hospital to check if there are mature follicles, if not, you can leave it untreated and wait for a week to see if you get your period. The follicle can be found in the shortest possible time oral emergency contraceptive pills, so as to avoid unwanted pregnancy leading to unnecessary trouble. Menstruation itself is irregular, in their own projection is the week before menstruation, this case is even more inaccurate, the chances of accidental pregnancy is greater, or caution is best.