Taking Yutin, if there is no withdrawal bleeding, it does not clinically mean that it is a contraceptive failure. Because it is scheduled to be a highly effective progestin, if it is taken orally during the first half of the menstrual period, it will cause abnormal thickening of the endometrium, which will prevent the fertilized egg from being laid and achieve the purpose of contraception in clinical practice. When yutin is discontinued, this exogenous progestin appears to withdraw, and the endometrium loses the support of exogenous progestin, and withdrawal bleeding occurs. And in the second half of the menstrual period when oral Yuktin is taken, the endometrium already appears to be thickened by the action of the corpus luteum. When stopping the use of yutin, the endometrium is not overly sensitive to stop yutin taking, so there will be no withdrawal bleeding, and this situation does not mean that contraception is a failure.