Will the Mirena (levonorgestrel-releasing intrauterine system) decrease the risk of ectopic pregnancy in a patient with a history of bilateral fallopian tube fimbriectomy?

Mirena and Ectopic Pregnancy Risk After Bilateral Fimbriectomy

In a patient with bilateral fimbriectomy (removal of the fimbriae), the Mirena IUD will not decrease the risk of ectopic pregnancy because the patient has already had surgical sterilization that dramatically reduces the absolute risk of any pregnancy—the Mirena would only provide contraceptive benefit if the tubes were to recanalize, and in that scenario, the relative risk of ectopic pregnancy would actually be higher if conception occurred with the IUD in place.

Understanding the Clinical Context

Baseline Risk After Fimbriectomy

• Bilateral fimbriectomy is a form of surgical sterilization that removes the fimbriated ends of the fallopian tubes, which are essential for ovum capture 1
• This procedure already provides highly effective contraception by preventing the egg from entering the fallopian tube
• The absolute risk of any pregnancy after bilateral fimbriectomy is already extremely low

How Mirena Affects Ectopic Pregnancy Risk

The Paradox of IUD Use and Ectopic Pregnancy:

• Absolute risk perspective: The Mirena IUD has a failure rate of less than 1% annually and provides excellent contraceptive protection, making the absolute risk of any pregnancy (including ectopic) extremely low 2

• Relative risk perspective: When pregnancy does occur with an IUD in place, approximately 1 in 20 pregnancies (5%) will be ectopic because IUDs prevent intrauterine pregnancies more effectively than ectopic pregnancies 2

• The CDC emphasizes that when a woman becomes pregnant during IUD use, the relative likelihood of ectopic pregnancy increases greatly, even though the absolute risk remains extremely low 1, 2

Dose-Dependent Considerations

Recent evidence shows important differences between levonorgestrel doses:

• The 52-mg Mirena has a Pearl Index for ectopic pregnancy of 0.009 (95% CI 0.006-0.014) 3
• Lower-dose formulations (13.5 mg and 19.5 mg) have significantly higher ectopic pregnancy rates, with the 13.5-mg showing a Pearl Index of 0.136 3, 4
• The relative risk for ectopic pregnancy with 13.5-mg LNG-IUS is 14.49 times higher than the 52-mg formulation 3

Clinical Decision-Making Algorithm

For a patient with bilateral fimbriectomy:

1. Assess the need for contraception: If the fimbriectomy was complete and successful, additional contraception is generally unnecessary

2. Consider non-contraceptive benefits: The Mirena may still be appropriate for managing heavy menstrual bleeding (reduces menstrual blood loss by 40-50%) or dysmenorrhea, not for contraception 1

3. If tubes could recanalize: In the rare scenario where tubal recanalization is a concern, the Mirena would provide contraceptive benefit, but with the caveat that any breakthrough pregnancy would have a higher relative risk of being ectopic 2

Critical Clinical Caveat

The key pitfall is misunderstanding risk types: The Mirena doesn't "increase" ectopic pregnancy risk in absolute terms—it dramatically reduces all pregnancy risk. However, if pregnancy occurs despite the IUD, the proportion that are ectopic is higher because the IUD is better at preventing intrauterine than ectopic implantation 2, 5.

In your specific patient with bilateral fimbriectomy, the Mirena would be redundant for contraception and would not provide additional protection against ectopic pregnancy beyond what the surgical sterilization already provides.