The common reasons for the presence of brown blood in the week before menstruation are as follows: 1, if a woman of childbearing age, with normal sexual life, the first thing to do is to determine whether or not to be pregnant, you can use the early pregnancy test paper at home to detect. If there is indeed pregnancy, you should go to the hospital in time to check the blood and further treatment; 2, there is gynecological inflammation exists, may also cause a small amount of blood in the week before menstruation, then you can clean up after menstruation and then carry out leukorrhea examination, or check the blood related indicators; 3, the luteal function is insufficient, because the week before menstruation happens to be the luteal phase, the luteal phase is the latter part of the menstrual cycle, the luteal body is formed after ovulation, to maintain the female hormone levels. If this function is insufficient, instability of the lining can also cause blood to appear. Hormone checks can be done about a week before menstruation to check for adequate progesterone levels. If it is sufficient, you can continue to observe; if it is insufficient, it may be related to low progesterone and can be treated with appropriate progesterone supplementation.