During the menstrual cycle, the lining of the uterus thickens reason being it is ready for pregnancy. During period, the uterus lining along with blood is shed by the body. Near the end of the period or the start, sometimes the menstrual blood becomes dark brown or almost black. Darker-colored blood usually just means that the blood is going out of the body at a slower rate i.e. blood flow is not heavy or it could be old blood. Sometimes the reasons can be that blood was stuck in uterus folds or the periods are not that frequent.
Some of the reasons for dark colored blood are:
- Large uterus:
During pregnancy sometimes if the uterus gets stretched and may not return to its original size as before and may get permanently enlarged. This may result in blood clotting as it gets time to collect before it’s discharged from the body. This results in a black color period blood.
- Obstruction of menstrual blood:
Anything obstructing the flow of period blood from the uterus by blocking it or stopping it to pass through the cervix and then out from vagina can cause problems of color of period blood.
- Retained menses:
It may be because the menses could not come out of uterus or even the vagina. An imperforate hymen is where the hymen obstructs the vagina by covering it completely or partially and as a result during menarche, the menses doesn’t pass out through the vagina. With older women, the obstruction or slowing down the passage of menses from the uterus may be because of narrowing of the cervix or the endocervical canal. And hence the darkening of period blood takes place. There can be other anatomical abnormalities of uterus, cervix or vagina which can be birth defects causing dark color menstrual flow.
- A miscarriage:
A miscarriage can be a common cause of brown to black vaginal bleeding. Not all the women realize that they are pregnant until there is an abnormally heavy bleed particularly consisting of large clots or the color varying from the normal period blood. Sometimes the products of conception are retained in the body and not ejected out of the body which is known as a missed abortion. This happens when the cervical os does not allow the products of conception to pass out of the body. With the passage of time there can be a scanty brown to black bleed with foul smell.
- Dark period blood can be a result of some kind of infections of the vagina, cervix or uterus by the proteolytic enzymes of the bacteria rapidly degrading the blood. Usually these infections may be sexually transmitted like gonorrhea and chlamydia, common cause being rectal bacteria called E.coli or due to overgrowth of the bacteria in the vagina which occurs naturally i.e. vaginosis. Common symptoms of this could be foul smelling discharge, pelvic pain during urination and sexual activity like intercourse and sometimes followed by a fever.
- If ulcer formation takes place in the reproductive tract it may cause bleeding and if the passage is blocked or obstructed with pelvic inflammatory disease or infection then there may be a dark brown to black vaginal bleed usually presenting as spotting.
When to see a doctor?
- A pregnant woman having a brown to black vaginal bleed and if it is accompanied by abdominal pain should get herself investigated immediately.
- Temporary thick black flow isn’t necessarily a cause for concern. But, regular heavy periods need a trip to the doctor to check your blood counts and rule out the possibilities of any abnormalities.