Before implantation, artificial menstrual cycles are created by giving the woman estrogen and progesterone, to rejuvenate the lining of the uterus and increase the chances of a successful pregnancy. Abnormal Uterine Bleeding Uterine bleeding may be abnormally heavy, light, frequent, or irregular or may occur abnormally after menopause. In about 25 percent of the women who have abnormal bleeding, it's caused by a physical disorder. Bleeding from the vagina before puberty and after menopause is almost always abnormal. Tumors of the ovaries occasionally cause bleeding from the vagina, but usually only if they produce hormones.
Age is an important factor in determining the likely cause of uterine bleeding.
Pubic hair and breasts are obvious signs that puberty has begun. Precocious puberty may be caused by certain drugs, brain abnormalities, low thyroid hormone levels, or hormone-producing tumors of the adrenal glands or ovaries. In most cases, however, the cause is unknown. Girls with vaginal adenosis have an increased risk of developing cancer of the vagina and cervix later in life. Cancer may cause bleeding in this age group, but not commonly.