If the leucorrhea is yellow when you are about to get your period, it may be caused by vaginitis, cervicitis, endometritis, pelvic inflammatory disease, or submucosal fibroids, which may also cause the leucorrhea to appear yellow. Under normal circumstances, the leucorrhea will increase before the menstruation, but the color will not be yellow, or normal milky white, because before the menstruation of the endometrial glands will appear to secrete a lot, so it will lead to an increase in vaginal secretions, which is a physiological phenomenon. However, if the color is yellow, it is a pathological phenomenon and should be treated actively after examination.