If you don’t have your period for half a year and then have it again, it’s usually a perimenopausal reaction, but it can’t be ruled out that it’s caused by polycystic ovary syndrome, so it’s recommended to consult a doctor in time to find out the cause. 1. Perimenopausal reaction: changes in menstruation are the earliest clinical symptom of perimenopausal period, mainly shortening of menstrual cycle, and some patients may have prolonged menstrual cycle. Therefore, when menstruation comes back after six months of menopause, it means that there is still the development of small follicles in the ovaries, and the development of such follicles will secrete estrogen and progesterone, which will promote the proliferation and secretion of the endometrium again, resulting in vaginal bleeding, i.e. the onset of menstruation. 2. Polycystic ovary syndrome: If the patient is in puberty or childbearing age, and the menstruation stops for half a year and comes back, it means that the ovary function is abnormal and ovulation is irregular, and the most common one is polycystic ovary syndrome, in which scanty menstruation is the main clinical manifestation, and it is the prolongation of menstruation cycle because of the polycystic change of the ovary and the irregularity of the ovulation. In addition, half a year without menstruation again may also be caused by other factors, it is recommended that the patient timely visit the hospital for examination, to clarify the cause of the disease, and then follow the doctor’s instructions targeted treatment.