A woman who has intercourse on the first day of her period just after her period will not usually get pregnant. The menstrual period is between 3-7 days, and within eight days of the menstrual flow is a safe period, and you will not get pregnant in general. For women with a regular menstrual cycle, ovulation is on the 14th day before the menstrual period, and just after the menstrual period, it should be a safe period and the chance of pregnancy is very small. However, this is not absolute, as sperm can survive in the body for three days. The follicles may be discharged early or have abnormal ovulation. If you use the safe period for contraception for a long time, the chances of failure will be higher. Menstruation and ovulation can be affected by environmental factors, emotional stress, dietary factors, diseases, drugs, staying up late, cold stimulation, etc. So it is not absolutely impossible to get pregnant just after the menstruation, and you should usually take good contraceptive measures.