The Levonorgestrel-releasing intrauterine system (LNG-IUS/Mirena) has a Pearl Index of approximately 0.1–0.2 per 100 woman-years. Its contraceptive mechanism is PRIMARILY:

• A Inhibition of ovulation through suppression of the hypothalamo-pituitary axis
• B Copper ion-mediated spermicidal effect
• C Thickening of cervical mucus and endometrial atrophy preventing implantation, with inconsistent ovulation suppression ✓
• D Tubal spasm preventing fertilisation

Explanation

LNG-IUS primarily acts through local (intrauterine) effects: very high local levonorgestrel concentration causes profound endometrial decidualisation and subsequent atrophy (preventing implantation), and markedly thickens cervical mucus (preventing sperm penetration). Ovulation suppression is inconsistent — 50–75% of cycles remain ovulatory — so contraception is predominantly non-ovulatory in mechanism. Copper IUS works via spermicidal copper ions. LNG-IUS also has therapeutic uses in menorrhagia and endometriosis.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.