Best Contraception to Prevent Ectopic Pregnancy
Both OCPs and IUDs dramatically reduce the absolute risk of ectopic pregnancy compared to no contraception, but the levonorgestrel-releasing IUD (LNG-IUD) provides superior protection against ectopic pregnancy compared to both copper IUDs and OCPs, with the highest-dose LNG-IUD (52 mg) offering the lowest ectopic pregnancy rate. 1, 2, 3
Understanding the Paradox
The key concept is that the absolute risk of ectopic pregnancy is extremely low with any IUD because of their high contraceptive effectiveness 1. However, when pregnancy does occur during IUD use, the relative likelihood of it being ectopic increases greatly 1. This does not mean IUDs cause ectopic pregnancy—rather, they prevent intrauterine pregnancy more effectively than ectopic pregnancy.
Comparative Effectiveness Data
LNG-IUD vs Copper IUD
The LNG-IUD demonstrates significantly lower ectopic pregnancy rates than copper IUDs:
- In a large European prospective study of 58,324 IUD users, the LNG-IUD showed an adjusted hazard ratio for ectopic pregnancy of 0.26 (95% CI: 0.10-0.66) compared to copper IUDs 2
- This means LNG-IUD users have approximately 74% lower risk of ectopic pregnancy compared to copper IUD users 2
- The LNG-IUD may reduce the rate of ectopic pregnancy compared to copper IUDs 4
Dose Matters for LNG-IUDs
Among LNG-IUDs, higher hormone doses provide better protection against ectopic pregnancy:
- The 52-mg LNG-IUS has a Pearl Index for ectopic pregnancy of 0.009 (95% CI 0.006-0.014) 3
- The 19.5-mg LNG-IUS has a Pearl Index of 0.037 (95% CI 0.021-0.067)—approximately 4.4 times higher risk than the 52-mg version 3
- The 13.5-mg LNG-IUS has a Pearl Index of 0.136 (95% CI 0.106-0.176)—approximately 14.5 times higher risk than the 52-mg version 3
Clinical Recommendation Algorithm
For women specifically concerned about ectopic pregnancy prevention:
First choice: 52-mg LNG-IUD - provides the lowest absolute risk of ectopic pregnancy among all contraceptive options 3
Second choice: Lower-dose LNG-IUD (19.5 mg or 13.5 mg) - still superior to copper IUDs and OCPs, though less protective than the 52-mg version 3
Third choice: Copper IUD - highly effective contraception with low absolute ectopic risk, but higher than LNG-IUDs 2
OCPs - effective contraception that reduces ectopic pregnancy risk compared to no contraception, but less protective than IUDs due to lower overall contraceptive efficacy
Critical Caveat for Women with Prior Ectopic Pregnancy
Past ectopic pregnancy is not a contraindication to IUD use 1. The CDC Medical Eligibility Criteria classifies both LNG-IUD and copper IUD as Category 1 (no restrictions) for women with past ectopic pregnancy 1. The comment emphasizes that while the absolute risk remains extremely low, when pregnancy does occur during IUD use, the relative likelihood of ectopic pregnancy increases 1.
For women with prior ectopic pregnancy who choose an IUD, the 52-mg LNG-IUD should be strongly preferred to minimize the already-low risk 3.
Why This Matters Clinically
The mechanism explains the superiority: LNG-IUDs work primarily through local endometrial effects and cervical mucus thickening, which prevents sperm from reaching the fallopian tubes 4. This prevents fertilization entirely, thereby preventing both intrauterine and ectopic pregnancies. Copper IUDs work primarily by preventing implantation, which is less effective at preventing tubal pregnancies 2.