Does a levonorgestrel (LNG) intrauterine device (IUD) stop ovulation?

Effect of LNG-IUD on Ovulation

The levonorgestrel intrauterine device (LNG-IUD) primarily works through local effects in the uterus and generally does not stop ovulation in most users. 1, 2

Mechanism of Action

• The LNG-IUD releases levonorgestrel directly into the uterine cavity at an initial rate of 20 μg per day, creating high hormone levels in the endometrium but low levels in systemic circulation 1
• Primary contraceptive effects include:
  • Strong endometrial suppression (making the endometrium thin and inactive) 1, 3
  • Thickening of cervical mucus (becomes scanty and viscous) 1
  • Although ovulation may be disturbed to some degree in some women, estradiol production typically continues normally 1

Ovulatory Status with LNG-IUD

• Most women who use the LNG-IUD continue to ovulate, even those who experience amenorrhea 4
• The local release of levonorgestrel makes the endometrium insensitive to estradiol released from the ovaries, but does not consistently prevent ovulation 3, 4
• The contraceptive efficacy of the LNG-IUD does not rely on inhibition of ovulation but rather on its local effects on the endometrium and cervical mucus 2, 5

Bleeding Patterns and Relation to Ovulation

• Approximately half of LNG-IUD users experience amenorrhea or oligomenorrhea by 2 years of use 6, 7
• Despite the absence of menstrual bleeding in many users, most continue to ovulate normally 4
• Unscheduled spotting or light bleeding is common during the first 3-6 months of use but generally decreases with continued use 7, 8
• Over time, bleeding generally decreases, with many women experiencing only light menstrual bleeding or amenorrhea 6, 7

Clinical Implications

• The LNG-IUD has a Pearl index (failure rate) of approximately 0.1-0.2 per 100 woman-years, making it one of the most effective contraceptive methods available 1, 3
• The high contraceptive efficacy is maintained despite continued ovulation in most users, demonstrating that ovulation inhibition is not necessary for its effectiveness 1, 5
• The LNG-IUD provides protection against ectopic pregnancy with rates as low as 0.02 per 1000 users per year 1, 3
• Return to fertility is rapid after removal of the LNG-IUD 5

Important Considerations for Patient Counseling

• Women should be counseled that the LNG-IUD primarily works through local effects rather than by stopping ovulation 1, 2
• Patients should understand that changes in bleeding patterns (including amenorrhea) do not indicate lack of ovulation or decreased fertility after removal 4, 5
• Pre-insertion counseling about expected bleeding pattern changes is crucial for improving user satisfaction and continuation rates 4