Risk of Ectopic Pregnancy with Progestin-Only Contraception
Progestin-only contraceptives dramatically reduce the absolute risk of ectopic pregnancy by being highly effective at preventing all pregnancies, but if contraceptive failure occurs, the proportion of pregnancies that are ectopic is substantially higher than in the general population. 1, 2
Understanding the Paradox: Absolute vs. Relative Risk
The key to understanding ectopic pregnancy risk with progestin contraception lies in distinguishing between two concepts:
- Absolute risk of ectopic pregnancy is extremely low because these methods are highly effective at preventing pregnancy overall 1
- However, when method failure occurs, the proportion of those pregnancies that are ectopic is higher compared to combined hormonal contraceptives or no contraception 3
The CDC explicitly states: "The absolute risk for ectopic pregnancy is extremely low because of the high effectiveness of IUDs. However, when a woman becomes pregnant during IUD use, the relative likelihood of ectopic pregnancy increases greatly." 1 This principle applies to all progestin-only methods.
Specific Incidence Rates by Method Type
Progestin-Only Pills
- Low-dose progestin pills (norethisterone 0.35 mg, lynestrenol 0.5 mg): 0.81 ectopic pregnancies per 1,000 woman-years 4
- Medium-dose progestin pills (desogestrel 75 mg): 0.24 ectopic pregnancies per 1,000 woman-years 4
- When pregnancy occurs on progestin-only pills, the proportion of ectopic pregnancies ranges from 1:2 to 1:21 3
Progestin Implants
- Etonogestrel implants: 0.31 ectopic pregnancies per 1,000 woman-years 4
- Levonorgestrel implants: 0 to 2.9 ectopic pregnancies per 1,000 woman-years 2
- Few ectopic pregnancies reported overall due to high contraceptive efficacy 2
Progestin Injectable (DMPA)
- Very few ectopic pregnancies reported in studies 2
- Specific incidence rates not well-established due to high method effectiveness 2
Progestin IUDs
- 52-mg levonorgestrel IUD: 0.30 ectopic pregnancies per 1,000 woman-years 4
- 13.5-mg levonorgestrel IUD: 2.76 ectopic pregnancies per 1,000 woman-years—substantially higher than other hormonal methods 4
Comparison to Other Methods
For context, the absolute incidence rates are:
- Combined oral contraceptives: 0.20 per 1,000 woman-years—lower than most progestin-only methods 4
- No contraception: 2.6 per 1,000 woman-years—much higher than any contraceptive method 5
- Oral contraceptives or vasectomy: 0.005 per 1,000 woman-years (lowest risk) 5
Clinical Implications and Counseling Points
Key Message for Patients
Women using progestin-only contraception should understand that while their overall risk of ectopic pregnancy is very low due to excellent pregnancy prevention, if they do become pregnant while using the method, there is a higher chance that pregnancy will be ectopic compared to other contraceptive failures. 1, 2, 3
When to Suspect Ectopic Pregnancy
- Any woman with a positive pregnancy test while using progestin-only contraception requires prompt evaluation for ectopic pregnancy 1
- The CDC recommends advising women to have a pregnancy test if they do not have withdrawal bleeding within 3 weeks after emergency contraception use 1
Common Pitfall to Avoid
Do not deny women access to progestin-only methods due to ectopic pregnancy concerns—the absolute risk remains extremely low, and these methods provide excellent overall pregnancy prevention 2. The statement "risk of ectopic pregnancy should not be a deterrent for use or provision of these methods" is explicitly made in the research literature 2.
History of Prior Ectopic Pregnancy
Women with a history of ectopic pregnancy can use progestin-only methods without restriction (U.S. MEC Category 1 for both LNG-IUD and Cu-IUD) 1. The absolute risk remains extremely low due to high contraceptive effectiveness 1.
Method Selection Considerations
For women concerned about ectopic pregnancy risk, combined oral contraceptives have the lowest incidence rate (0.20 per 1,000 woman-years), followed by medium-dose progestin pills (0.24 per 1,000 woman-years) and progestin implants (0.31 per 1,000 woman-years). 4 The 13.5-mg levonorgestrel IUD should be avoided if ectopic pregnancy risk is a primary concern, as its rate is substantially higher than other hormonal methods 4.