What causes bleeding with Mirena (levonorgestrel-releasing intrauterine system)?

Causes of Bleeding with Mirena (Levonorgestrel-releasing Intrauterine System)

Irregular bleeding with Mirena is most commonly due to normal hormonal adjustment during the first 3-6 months of use, but can also be caused by IUD displacement, infection, pregnancy, or underlying uterine pathology. 1

Normal Bleeding Patterns with Mirena

• Initial adjustment period: Spotting or irregular bleeding is very common during the first 3-6 months of Mirena use 2, 3
• Long-term patterns: After 6-12 months of use, bleeding typically improves with:
  • Amenorrhea in approximately 50% of users by 12-24 months 3
  • Spotting in 8-11% of users after 18-24 months 3
  • Oligomenorrhea (light, infrequent bleeding) in about 25% of users 3

Pathological Causes of Bleeding with Mirena

When bleeding with Mirena is persistent, heavy, or develops after a period of stable bleeding patterns, consider these potential causes:

1. IUD displacement or expulsion 2, 1

   • Partial or complete expulsion can cause irregular or heavy bleeding
   • Check for presence of IUD strings; if strings are missing or longer than expected, consider ultrasound to confirm proper placement

2. Infection 2, 1

   • Sexually transmitted infections or pelvic inflammatory disease (PID)
   • Risk of PID is highest in the first 20 days after insertion 2
   • Symptoms may include unusual discharge, fever, or pelvic pain

3. Pregnancy (intrauterine or ectopic) 1

   • Although rare with Mirena (failure rate 0.1-0.2%), pregnancy should always be ruled out 1

4. Underlying gynecological conditions 2, 1

   • Uterine polyps or fibroids
   • Endometrial hyperplasia
   • Cervical or endometrial cancer (rare but important to exclude) 4, 5
   • These conditions may be masked by expected irregular bleeding patterns with Mirena

Warning Signs Requiring Immediate Evaluation

• Heavy bleeding that soaks through one or more pads/tampons per hour
• Severe abdominal pain
• Fever or unusual vaginal discharge
• Missing IUD strings or feeling the hard plastic of the IUD 1

Management of Problematic Bleeding

For persistent problematic bleeding with Mirena:

1. Rule out complications through physical examination and appropriate testing 2, 1
2. Consider medical management for bleeding during Mirena use:
   • NSAIDs (ibuprofen, naproxen) for 5-7 days during bleeding episodes 2, 1
3. If bleeding persists and is unacceptable to the patient:
   • Consider alternative contraceptive methods 2
   • Discuss removal of the Mirena if bleeding is intolerable

Important Clinical Considerations

• Irregular bleeding is the most common reason for Mirena discontinuation, particularly in the first 6 months 3
• Proper evaluation of irregular bleeding, including cervical cytology, should be performed in all women with persistent abnormal bleeding with Mirena 4
• Women who had Mirena inserted for heavy menstrual bleeding may have higher rates of discontinuation due to bleeding issues 3
• When replacing one Mirena with another, bleeding patterns typically remain favorable, with median bleeding/spotting days decreasing after the initial insertion period 6

Always take persistent abnormal bleeding seriously, as it may occasionally mask serious underlying pathology such as cervical or endometrial cancer 4, 5. This is especially important in women over 35 or those with risk factors for gynecological malignancies.