What is the risk of ectopic pregnancy in a woman using an intrauterine device (IUD)?

Ectopic Pregnancy Risk with IUD Use

IUDs dramatically reduce the absolute risk of ectopic pregnancy compared to using no contraception, but when pregnancy does occur with an IUD in place, the relative likelihood that it will be ectopic increases substantially—approximately 5% (1 in 20) of IUD failures will be ectopic pregnancies. 1, 2, 3

Understanding the Paradox: Absolute vs. Relative Risk

The relationship between IUDs and ectopic pregnancy involves a critical distinction that often causes confusion:

Absolute Risk (Compared to No Contraception)

• IUDs provide excellent protection against ectopic pregnancy overall. Women using copper IUDs have a 91% reduction in ectopic pregnancy risk compared to women using no contraception (adjusted OR 0.09,95% CI 0.06-0.13). 4
• When compared to all women not using contraception, IUD users have significantly lower rates of ectopic pregnancy because IUDs are highly effective at preventing all pregnancies. 5, 6
• Past history of ectopic pregnancy is NOT a contraindication to IUD use (U.S. MEC Category 1—no restriction), precisely because the absolute risk remains extremely low. 1

Relative Risk (When Pregnancy Occurs)

• However, when contraceptive failure occurs with an IUD in situ, the pregnancy is disproportionately likely to be ectopic. 1, 2, 3
• This occurs because IUDs prevent intrauterine implantation more effectively than they prevent tubal implantation—the mechanism of action creates a hostile intrauterine environment but provides less protection against extrauterine pregnancy. 6
• Compared to pregnant controls (women who conceived), current IUD users have a 10-fold increased odds of ectopic pregnancy (pooled OR 10.63,95% CI 7.66-14.74). 5

IUD Type Matters: Dose-Dependent Risk

The levonorgestrel dose in hormonal IUDs significantly affects ectopic pregnancy risk:

• 52-mg LNG-IUD (Mirena): Pearl Index for ectopic pregnancy = 0.009 per 100 woman-years (lowest risk) 7, 8
• 19.5-mg LNG-IUD: Pearl Index = 0.037 per 100 woman-years; 4.44-fold higher risk than 52-mg 7, 8
• 13.5-mg LNG-IUD: Pearl Index = 0.136 per 100 woman-years; 14.49-fold higher risk than 52-mg overall, and 20.59-fold higher in the first year 7, 8
• Copper IUD: Incidence rate approximately 0.30 per 1,000 woman-years 8

For women with known risk factors for ectopic pregnancy (prior ectopic, PID history, tubal surgery), higher-dose LNG-IUDs should be preferentially recommended. 7

Critical Clinical Management When Pregnancy Occurs with IUD

Immediate Evaluation

Any woman who becomes pregnant with an IUD in place must be immediately evaluated for ectopic pregnancy before any other management decisions. 1, 3

If Strings Visible and Pregnancy Desired

• The IUD should be removed as soon as possible by gently pulling on the strings to reduce risks of spontaneous abortion (including life-threatening septic abortion), preterm delivery, and chorioamnionitis. 1, 3
• Removal improves outcomes but does not reduce risks to baseline levels of pregnancy without an IUD. 1
• With LNG-IUDs left in place, 8 in 10 pregnancies end in spontaneous abortion. 3

If Strings Not Visible

• Perform or refer for ultrasound to locate the IUD (may have been expelled or perforated the uterine wall). 1
• If ultrasound unavailable or IUD confirmed intrauterine, counsel about significantly increased risks and need for close monitoring. 1

Warning Signs Requiring Immediate Return

Instruct patients to seek care promptly for: heavy bleeding, cramping, pain, abnormal vaginal discharge, or fever. 1, 3

Common Pitfalls to Avoid

• Do not reassure patients that IUDs increase ectopic pregnancy risk in absolute terms—this is incorrect and may deter appropriate contraceptive use. The absolute risk is extremely low. 1, 5, 4
• Do not fail to evaluate for ectopic pregnancy when IUD failure occurs—the relative risk is dramatically elevated and requires immediate assessment. 1, 2, 3
• Do not assume all LNG-IUDs carry equal ectopic pregnancy risk—lower-dose formulations have substantially higher rates. 7, 8
• Do not leave an IUD in place during desired pregnancy without counseling about the 80% spontaneous abortion rate with LNG-IUDs. 3