Menstrual blood is usually bright to dark red and may or may not have some clots. It should not be brown to black and if it is then it needs to be investigated further. The main reason why blood may appear these colors is due to degradation of the blood cells either due to exposure to air (oxidation) over time, the action of bacterial enzymes or exposure of blood to certain chemicals that may cause rapid degradation and discoloration. A brown to black vaginal bleed in a pregnant women particularly if it is accompanied by abdominal pain should be investigated immediately.
Source of the Bleeding
Normally menstrual blood arises from the uterus when inner lining (endometrium) is sloughed off and expelled as part of the menstrual cycle. This is known as menstruation. Abnormal vaginal bleeding may not always occur from the uterus or endometrium specifically.
The source of the bleeding may be from the vagina itself (including the vulvar), cervix, uterus (not only from the endometrium) and even the fallopian tubes. It is also important to distinguish between urinary tract infections (UTIs) since the latter may also cause bleeding and/or a brown discharge.
Causes of Brown to Black Vaginal Bleeding
It is important to ascertain whether the bleeding is related to a menstrual bleed or not. The presence of other symptoms like pain, discharge preceding or during the bleed, blood clots or pieces of tissue in the blood are all significant in identifying the most likely cause. Remember that a small quantity of brown blood towards the end of a menstrual period is not abnormal and is just degraded blood (“old blood”) being expelled. However, it should not persist for long periods.
Retained menses is not a common phenomenon. It may be due to the menses being retained with the uterus or even in the vagina. An imperforate hymen is where the hymen fully rather than partially covers the vagina and at the onset of menstruation during puberty (menarche), the menses cannot pass out of the vagina. An old tampon or a tampon that is not changed frequently may also be a consideration.
In older women, cervical stenosis which is narrowing of the cervix (or more correctly the endocervical canal) either obstructs or drastically slows down the exit of menses from the uterus. There are other possibly causes relating to anatomical abnormalities of the uterus, cervix or vagina but these are usually present from birth (congenital). However, in older women the presence of brown vaginal bleeding raises the concerns about other conditions like uterine cancer.
A miscarriage is a more common cause of brown to black vaginal bleeding. While it is a consideration in every pregnant woman’s mind, not all woman realize that they are pregnant until there is an abnormally heavy bleed particularly when it is laden with large clots or the color varies significantly from the normal menstrual blood. The products of conception are eventually ejected but sometimes it is retained.
This is known as a missed abortion and arises when the cervical os does not dilate to allow for the products of conception to pass out. Over time there is a scanty brown to black bleed that is often foul smelling. This symptom is less common with an elective / induced abortion if it is done by a medical professional since the cervix is dilated and the products of conception may be removed with dilatation and curettage (D&C).
Severe pain with signs of shock and abnormal vaginal bleeding in a female within her reproductive years can also be an ectopic pregnancy. It is a medical emergency and needs immediate attention.
Pelvic Inflammatory Disease (PID)
Infections of the vagina, cervix or uterus may cause brown to black vaginal bleeds at the proteolytic enzymes of the bacteria rapidly degrade the blood. These infections may be sexually transmitted like gonorrhea and chlamydia, commonly caused by rectal bacteria like E.coli or due to overgrowth of the naturally occurring bacteria in the vagina (vaginosis).
It is typically associated with a foul smelling discharge, pelvic pain with pain during urination and intercourse and sometimes a fever. Most of the infections that result in pelvic inflammatory disease (PID) are sexually transmitted with chlamydia and gonorrhea among the most common in the United States. It is only considered to be PID when it extends beyond the cervix to infect the uterus, fallopian tubes and/or ovaries.
Fibroids are masses of tissue that arise from the middle muscular layer of the uterus known as the myometrium. These growths are benign (non-cancerous). It is also known as leiomyomas. The exact cause is unknown but it appears to be associated with genetic factors and hormones.
Uterine fibroids are a common cause of abnormal vaginal bleeding. The periods may be unusually heavy and last longer than normal even extending beyond 7 days. There is usually some pressure or fullness experienced in the pelvic area and sometimes it may be painful. The presence of urinary symptoms like frequent urination at times leads to a misdiagnosis of a urinary tract infection.
Cancer is another cause of vaginal bleeding that is not related to menses – intermenstrual bleeding. It is, however, not a common cause of brown to black vaginal bleeding. An ulceration of the reproductive tract may cause bleeding and if the outflow is restricted or complicated with pelvic inflammatory disease (infection) then there may be a dark brown to black vaginal bleed usually presenting as spotting. Uterine and cervical cancer are more likely causes in this regard.
A short-lived brown to black vaginal discharge which resolves on its own and does not recur may not necessarily be anything serious. However, it is always advisable to have it checked, preferably by a gynecologist. When profuse and accompanied by pain that is worsening, dizziness and/or weakness then immediate medical attention is necessary. Sometimes the more serious causes of brown to black vaginal bleeding may present with little to no symptoms beyond the discharge.
Foul-smelling discharges should also be taken seriously as this may be a sign of pelvic inflammatory disease (PID). Untreated or delayed treatment of pelvic inflammatory disease remains one of the most common causes of female infertility. A fever, nausea and vomiting along with pelvic pain and discharge (whether it is blood or not) should also be treated as a medical emergency until proven otherwise.