Dark Menstrual Blood: Causes and Management
Dark menstrual blood is typically a normal physiological finding that represents older blood with prolonged endometrial contact, requiring reassurance rather than treatment in most cases.
Understanding Dark Menstrual Blood
Dark menstrual blood occurs when blood remains in the uterus longer before being expelled, allowing oxidation to darken its color from bright red to brown or nearly black. This is generally benign and does not indicate pathology.
When to Investigate Further
While dark blood alone is usually benign, investigate for underlying gynecological problems if accompanied by:
- Irregular bleeding patterns (spotting, prolonged bleeding, or heavy bleeding) that may indicate IUD displacement, sexually transmitted infections, pregnancy, or pathologic uterine conditions such as polyps or fibroids 1
- Heavy menstrual bleeding defined as flooding (changing pad/tampon more than hourly), clots ≥1 inch diameter, or low ferritin 2
- Structural abnormalities including endometrial polyps, submucosal fibroids, or adenomyosis, which should be evaluated with transvaginal ultrasonography or saline infusion sonohysterography 3
- Systemic symptoms suggesting thyroid dysfunction or hyperprolactinemia, which commonly cause ovulatory dysfunction 3
Diagnostic Workup for Concerning Presentations
If dark blood is accompanied by abnormal bleeding patterns:
- Rule out pregnancy with beta-hCG testing first 3
- Screen for sexually transmitted infections that can cause irregular bleeding 3
- Check thyroid function (TSH) and prolactin levels as these commonly cause ovulatory dysfunction 3
- Evaluate for coagulopathy in adolescents with menorrhagia or women with personal/family bleeding history, as up to 20% of women with heavy menstrual bleeding have an underlying inherited bleeding disorder 4, 5
Treatment Algorithm (Only if Pathology Identified)
For Irregular Bleeding with Identified Pathology
First-line treatment:
- NSAIDs for 5-7 days during bleeding episodes (mefenamic acid 500 mg three times daily, naproxen 440-550 mg every 12 hours, or ibuprofen 600-800 mg every 6-8 hours with food) reduce menstrual blood loss by 20-60% 3, 6
Second-line treatment:
- Combined hormonal contraceptives (oral pills, vaginal ring, or transdermal patch) to regulate cycles and reduce bleeding 3
- Low-dose COCs or estrogen for 10-20 days during bleeding episodes if NSAIDs fail 1
Most effective long-term option:
- Levonorgestrel-releasing intrauterine system (LNG-IUS) is the most effective medical treatment for menorrhagia, with efficacy comparable to endometrial ablation, though expect irregular spotting during the first 3-6 months 3, 4
For Contraceptive-Related Dark/Irregular Bleeding
- Amenorrhea or irregular bleeding from hormonal contraceptives requires no medical treatment—only reassurance and enhanced counseling about expected bleeding patterns, which significantly reduces discontinuation rates 7, 3
- If bleeding persists and is unacceptable to the patient, counsel on alternative contraceptive methods 1
Critical Pitfalls to Avoid
- Do not assume functional bleeding without excluding structural pathology, especially in women over 35 where polyps and fibroids become more common 3
- Never use aspirin for bleeding treatment as it may worsen bleeding 3
- Do not overlook coagulopathy screening in adolescents with menorrhagia or women with bleeding history, as von Willebrand disease affects up to 90% of women with underlying bleeding disorders 2, 8
- Abnormal uterine bleeding in perimenopausal/postmenopausal women should be considered malignancy until proven otherwise 5