If the 3rd is the first day of menstruation and the menstrual cycle is 28 days, the ovulation period is between the 13th and 22nd. If the menstruation is irregular, it can be judged according to the ovulation test paper, the nature of leukorrhea, ultrasound monitoring and other methods. The day of ovulation is generally 14 days before the next menstrual period, and the ovulation period refers to a period of 4 to 5 days before and after the day of ovulation. If the regular menstruation last menstruation is the 3rd, the menstrual cycle is 28 days, the next menstruation is the 1st, the ovulation period is between the 13th and 22nd. If menstruation is irregular, ovulation can be determined by ovulation test paper, changes in the nature of the leukorrhea during ovulation, ultrasound monitoring of the follicles, etc. However, ovulation does not necessarily occur at the time of ovulation, and it can be advanced or delayed. 4~5 days before and after ovulation is easy pregnancy, the rest of the time for the safe period, but the success rate of safe period contraception is often lower, the chance of unwanted pregnancy is high, it is recommended that women of childbearing age to take more efficient contraceptive methods, such as contraceptive rings, condoms, short-acting contraceptive pills and so on.