Generally speaking, after embryo transfer, taking or injecting progesterone will cause the menstrual cycle to be delayed, which is normal. Normally, after ovulation, the corpus luteum forms from the point of ovulation, and the corpus luteum secretes progesterone, i.e., luteinizing hormone, which maintains the body’s state of pregnancy and prevents menstruation. Embryo transfer needs to mimic the endocrine environment of pregnancy as much as possible, i.e. the corpus luteum has to secrete progesterone. Therefore, after embryo transfer, patients are usually required to continue taking progesterone, which can cause a delay in the menstrual cycle.