If a woman has a regular menstrual cycle, the safe period is usually 1-4 days after menstruation. This is when the follicles are growing and developing, and the follicles are small and not yet able to ovulate, so it is called the safe period. The safe period is relative, not absolute. If a woman has an irregular menstrual cycle or a shortened menstrual cycle, such as a period of about 22 days and a period lasting about 10 days, in this case, the follicle maturation period is 3-4 days after the woman’s period clears, and ovulation can occur when the follicle develops to about 2 cm. Therefore, if a woman does not want to get pregnant, it may not be safe to use a safe period contraceptive method and it is recommended to take a safer contraceptive measure.