Why are my menstrual periods dark brown?

Dark Brown Menstrual Blood: Causes and Implications

Dark brown menstrual blood is typically normal and usually represents older blood that has had time to oxidize, but it can sometimes indicate underlying conditions that require medical attention.

Normal Causes of Dark Brown Menstrual Blood

• Oxidized blood: When blood stays in the uterus longer before being expelled, it oxidizes and turns from bright red to dark brown
• Beginning or end of period: Brown discharge is common at the start or end of menstruation when flow is lighter and moves more slowly
• Hormonal fluctuations: Normal hormonal changes can affect the color and consistency of menstrual blood

Potential Medical Conditions Associated with Dark Brown Menstrual Blood

Ovulatory Dysfunction

Dark brown menstrual blood can be associated with ovulatory dysfunction, which is classified under the PALM-COEIN system for abnormal uterine bleeding 1. Ovulatory dysfunction may present with:

• Irregular menstrual cycles (less than 21 days or more than 35 days)
• Changes in flow volume and duration
• Hormonal imbalances affecting normal menstrual patterns

Polycystic Ovary Syndrome (PCOS)

PCOS affects approximately 8-13% of women 1 and can cause:

• Irregular menstrual cycles with dark brown bleeding
• Hyperandrogenism (excess male hormones)
• Insulin resistance and metabolic disorders
• Higher prevalence (10-25%) in women with temporal lobe epilepsy 1

Endometriosis

Present in approximately 2-10% of women of childbearing age 1, endometriosis can cause:

• Dark brown menstrual blood
• Chronic pelvic pain
• Dysmenorrhea (painful periods)
• Reduced fertility

Uterine Fibroids

Fibroids can alter menstrual blood color and are associated with:

• Heavy or prolonged bleeding that may appear dark brown
• Increased cardiovascular risk even without clinical hypertension 1
• Structural changes to the uterus affecting blood flow

When to Seek Medical Evaluation

Medical attention is warranted if dark brown menstrual blood is accompanied by:

• Heavy bleeding: Soaking through pads/tampons every 1-2 hours
• Prolonged bleeding: Periods lasting more than 7 days
• Severe pain: Not relieved by over-the-counter pain medications
• Irregular cycles: Consistently occurring less than 21 days or more than 35 days apart
• Intermenstrual bleeding: Bleeding between periods
• Associated symptoms: Fatigue, dizziness, shortness of breath (suggesting anemia)

Diagnostic Approach

If concerned about dark brown menstrual blood, evaluation may include:

• Hormonal assessment: Measuring LH, FSH, prolactin, progesterone, and testosterone levels 1
• Pelvic ultrasound: To identify structural abnormalities like fibroids, polyps, or endometrial thickening 1, 2
• Hysteroscopy: For visualization of the endometrial cavity if imaging suggests abnormalities 1
• Endometrial biopsy: Highly sensitive (99.6%) for detecting endometrial carcinoma in patients with risk factors 2
• Blood count: To check for anemia if heavy bleeding is present 3

Management Options

Management depends on the underlying cause:

For Hormonal Imbalances/Ovulatory Dysfunction:

• Hormonal contraceptives: Combined hormonal contraceptives or progestin-only options 1, 2
• Levonorgestrel IUD: Excellent option for abnormal uterine bleeding with approximately 50% of users experiencing amenorrhea or oligomenorrhea by 2 years 2

For Heavy Bleeding:

• Tranexamic acid: Effective for reducing blood loss 2, 3
• NSAIDs: Such as ibuprofen 600-800mg every 6-8 hours with food for the first 24-48 hours of symptoms 2
• Iron supplementation: For patients with iron-deficiency anemia 3

For Structural Abnormalities:

• Surgical options: Including hysteroscopic procedures, endometrial ablation, or hysterectomy for persistent cases not responding to medical management 1, 3

Prevention and Self-Care

• Maintain a menstrual calendar to track cycle length, regularity, and bleeding characteristics
• Consider lifestyle factors that may affect hormonal balance (stress, extreme exercise, significant weight changes)
• Ensure proper nutrition with adequate iron intake if experiencing heavy periods
• Practice good menstrual hygiene with proper disposal of used absorbent materials 2

Dark brown menstrual blood is often normal, but persistent changes in menstrual patterns warrant medical evaluation to rule out underlying conditions that may require treatment.