Which Contraception Options Prevent 99/100 Women from Getting Pregnant?
Both Mirena (B) and Nexplanon (C) prevent 99 out of 100 women from getting pregnant, with typical use failure rates of 0.2% and 0.05% respectively, making them the most effective reversible contraceptive options available. 1
Comparative Efficacy Data
Most Effective Options (>99% Efficacy)
Nexplanon (etonogestrel implant):
- Typical use failure rate: 0.05% (5 pregnancies per 10,000 women) 1
- Perfect use failure rate: 0.05% 1
- This translates to 99.95% effectiveness, preventing pregnancy in more than 99 out of 100 women 1
Mirena (levonorgestrel IUD):
- Typical use failure rate: 0.2% (20 pregnancies per 10,000 women) 1
- Perfect use failure rate: 0.2% 1
- This translates to 99.8% effectiveness, preventing pregnancy in more than 99 out of 100 women 1
Less Effective Options (<99% Efficacy)
Depo-Provera (medroxyprogesterone acetate injection):
- Typical use failure rate: 3-6% 1
- Perfect use failure rate: 0.2-0.3% 1
- This translates to 94-97% effectiveness with typical use, meaning it prevents pregnancy in approximately 94-97 out of 100 women, not 99 out of 100 1
NuvaRing (etonogestrel/ethinyl estradiol vaginal ring):
- Typical use failure rate: 8-9% 1
- Perfect use failure rate: 0.3% 1
- This translates to 91-92% effectiveness with typical use, meaning it prevents pregnancy in approximately 91-92 out of 100 women, not 99 out of 100 1
Clinical Significance of Long-Acting Reversible Contraception (LARC)
Both Nexplanon and Mirena are classified as LARC methods, which are the most effective reversible contraceptive options because their efficacy does not depend on user adherence. 1 The American Academy of Pediatrics specifically recommends counseling patients about LARC methods first when discussing contraceptive options, ordered from most to least effective. 1
Key Advantages of LARC Methods:
- Typical use and perfect use failure rates are nearly identical because they don't require daily adherence 1
- Extended duration of protection (3 years for Nexplanon, 5-8 years for Mirena) 1, 2, 3
- Rapid return to fertility after removal 1, 3
- Higher continuation rates at 1 year (80-84%) compared to other methods 1
Important Clinical Caveats
The distinction between typical use and perfect use is critical for patient counseling. 1 While Depo-Provera has a perfect use failure rate of 0.2-0.3% (similar to Mirena), its typical use failure rate is significantly higher at 3-6% because it requires injections every 12-13 weeks. 1, 4 Missing or delaying injections substantially reduces efficacy. 4
NuvaRing similarly shows a large gap between perfect use (0.3%) and typical use (8-9%) failure rates because it requires correct insertion, timely replacement every 3 weeks, and proper storage. 1, 5 User error significantly impacts its real-world effectiveness. 5
Recent research demonstrates that both Nexplanon and Mirena maintain their high efficacy beyond their FDA-approved durations, with Nexplanon remaining effective through 5 years 2, 6 and Mirena through 8 years. 3 This extended efficacy further enhances their cost-effectiveness and reduces the need for replacement procedures. 2, 3