Blood draws do not affect the normal menstrual flow because the amount of blood drawn is very small and it does not affect menstruation. The normal menstrual flow is closely related to the function of the hypothalamus, pituitary gland and ovaries. When there is a problem with any of the hypothalamus, pituitary gland and ovaries, abnormal menstruation can occur. When menstruation is abnormal, we have to look for the causes in these three areas, but of course the most common cause is a problem with the ovarian secretion function. If we want to know the basic secretion function of the ovaries, we can go to the hospital during the menstrual period, preferably 2-4 days, to have a blood test for hormone 6, which can directly reflect the secretion function of the ovaries. Menstrual disorders can be manifested in various ways, including irregular menstrual cycles, prolonged or shortened menstrual periods, all of which are called menstrual disorders. When menstrual disorders occur, it is best to go to the hospital and undergo some relevant tests, such as blood tests or gynecological ultrasound, and then give the appropriate treatment plan according to the results of these tests.