Retreating bleeding is often clinically indicated by the loss of progesterone support in the endometrium due to the withdrawal of exogenous progesterone, but it does not indicate pregnancy. In clinical practice, it is common to experience withdrawal bleeding when taking oral emergency contraceptives. This is because the emergency contraceptive pill is a highly effective progestogen that causes the endometrium to thicken abnormally. After stopping the pill, the endometrium loses the support of exogenous progesterone, and then there will be withdrawal bleeding, which usually lasts about 3-5 days and will be less than the amount of menstruation. In addition, if oral progestin is used to treat luteal insufficiency or to induce menstruation, withdrawal bleeding may also occur after stopping the pill.