Dark Period Blood: 6 Causes & When to See the Doctor

May 2022

Generally, small quantities of dark blood during a period is normal and does not indicate any health problems. especially if it occurs at the beginning or end of a period. However, it occurs frequently, it can be a sign of hormonal changes, uterine problems, stress or a sexually transmitted infection.

This can also happen when taking a birth control pill for the first time, when birth control is changed, or if the morning-after pill is taken. In these cases, menstruation can also become darker or have a coffee ground texture, but it usually returns to normal by the next cycle.

If the color of your period blood changes from its norm, or if it you have any concerns about how it looks, you should consult your family doctor or gynecologist. They can assess for any abnormalities and intiate treatment as necessary.

Main causes of dark period blood

Menstruation blood which is black, brown, or similar to coffee grounds may be caused by:

1. Pregnancy

A small amount of pink, brown or dark red bleeding is common in the first weeks of pregnancy as the embryo attaches to the walls of the uterus.

However, when this bleeding occurs at a later stage of pregnancy or is accompanied by other symptoms such as abdominal pain, shoulder pain, dizziness or excessive fatigue, it may indicate an ectopic pregnancy or miscarriage. You should be assessed immediately if you have any of these symptoms to rule out any problems.

Learn more about what can cause brown discharge during pregnancy.

2. Emotional changes

Some changes in a woman's emotional state, such as increased stress or depression, can affect the structure of the uterus by reducing the thickness of its walls. This change delays shedding of the uterine lining in preparation for menstruation, and blood has more time to become oxidized making it darker in color.

3. Hormonal changes

Hormonal changes, which can happen with thyroid problems or menopause, can cause small amounts of dark period blood. This change is also very common when switching birth control or when recently post-partum women start weaning from breastfeeding.

4. Sexually transmitted infections

Sexually transmitted infections caused by bacteria, such as gonorrhea or chlamydia, cause a more rapid breakdown of menstrual blood, which makes it darker. This type of blood is usually also accompanied by a foul smell, brown discharge before or after menstruation, pelvic pain and a fever above 38º C.

5. Endometriosis and other conditions

Endometriosis is the growth of endometrial tissue outside the uterus. This type of problem, or other conditions like adenomyosis, can cause severe pain in the pelvic region and dark discharge, similar to coffee grounds, that can occur both during and between menstruation.

In these cases, the period, besides being dark, can also last up to 7 days. In case of suspicion, you should go to the gynecologist for assessment and treatment as necessary (which may include surgery).

6. Post-partum

During the post-partum stage, dark blood is also an expected, normal finding. The uterus takes about 45 days to return to its normal size and bleeding typically happens during this time. This bleeding isn’t exactly menstruation, but it can be dark in color, and may confuse many women.

If you experience a period with dark blood and clots, read about the  7 reasons for menstrual blood clots.

When should you go to the doctor?

Changes in menstrual bleeding are usually normal and do not indicate problems, but you should go to the gynecologist if you have other symptoms, such as:

  • Period lasting more than 7 days
  • No period for more than 3 months
  • Vaginal bleeding between periods
  • Vaginal pain
  • Fever above 38º C or 100.4º F
  • Dizziness
  • Pale skin throughout the body or below the nails.

It is also important to remember that in cases of suspected pregnancy, the appearance of dark bleeding, with clots or in large quantities, is also a reason to see the doctor, because it may be a miscarriage, and a curettage may be necessary to clean the uterus.

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Edited by Tua Saude editing team in May 2022. Medical review completed by Dr. Sheila Sedicias - Gynecologist in November 2018.
Medical review:
Dr. Sheila Sedicias
Gynecologist
Physician graduated in Mastology and Gynecology by UFPE in 2008 and member no. 17459 of CRM-PE, Brazil.