Vaginal blood clots are thick collections of blood and uterine lining. These clots are expelled during menstruation and are usually seen on the days that a woman’s period is heaviest. In most cases, the woman’s body releases natural anticoagulants during menstruation, preventing formation of the clots. There are however, many reasons for these clots to occur, including miscarriage, abnormal growth of the lining of the uterus, the onset of menopause, or even just a particularly heavy period.
During normal menstruation, the lining of the uterus, also called the endometrium, is shed from a woman’s body through her vagina. Though the endometrium contains special enzymes that usually prevent blood clots from forming, it is not uncommon for women to have the occasional clot along with their normal menstrual blood. These clots are made up of blood cells that have stuck together. It is also possible for pieces of uterine lining to come through the vagina, undissolved, and often having the appearance of a vaginal blood clot, though they are made up of mostly endometrium and not blood.
Under normal circumstances, a woman can expect to have some vaginal blood clots on the heaviest days of her period. Clots that are less than 1 inch (25 mm) across usually cause no problems, though if there are many clots of this size, the woman should be seen by a doctor. A consistently heavy period with many clots can lead to anemia.
It is common for a woman to have many clots after she has given birth. It can take a week or more to shed the uterine lining after a baby is born, and blood clots are commonly seen as the last of the tissue is expelled. A woman who notices them while she is pregnant should see a doctor immediately, as blood clots are a common sign of miscarriage.
A number of abnormal conditions can cause vaginal blood clots to form as well. For the most part, clots appear because there is an unusual amount of endometrium, such as when benign uterine tumors called fibroids are present, or when adenomyosis or endometriosis have developed. Menopause can also create particularly heavy periods with many blood clots. In all of these cases, if the vaginal blood clots are large, numerous, or continue for a few menstrual cycles, the woman should be seen by a doctor to make sure that she is healthy.