It is not normal for menstruation to come once in 19 days occasionally. Normal menstrual cycle is 21~35 days, short interval between menstruation may be related to sex hormone secretion disorder, thyroid function abnormality and so on. 1. Sex hormone secretion disorder: Sex hormone secretion disorder refers to the dysfunction of the regulation of the hypothalamic-pituitary-ovarian axis. Menstruation is the cyclic shedding of the endometrium under the influence of estrogen and progesterone, and the secretion of estrogen and progesterone is regulated by the hypothalamus-pituitary-ovarian axis, so endocrine disorders will lead to abnormal menstruation. 2. Abnormal thyroid function: the thyroid gland can secrete thyroid hormones, if a woman has abnormal thyroid function, it will also have an effect on menstruation, which will lead to menstrual disorders. There may be other reasons for women to have menstruation once in 19 days, so it is recommended to go to the hospital in time for examination to clarify the cause of the problem and then treat the symptoms.