Most Likely Predisposing Factor for Ectopic Pregnancy
Pelvic inflammatory disease (PID) is the most likely predisposing factor among the options listed, as it represents the most common population-level risk factor for ectopic pregnancy, with risk doubling with each recurrent episode due to progressive tubal occlusion. 1, 2
Understanding the Risk Factor Hierarchy
While the question asks for the "most likely" predisposing factor, this requires distinguishing between the strongest individual risk versus the most common population-level risk:
Highest Individual Risk (But Less Common)
- Previous tubal pregnancy carries a 10-20% recurrence risk and represents one of the strongest individual risk factors 1, 3
- Tubal surgery (including sterilization) actually carries the highest individual risk for ectopic pregnancy 1, 2
- However, these factors are less prevalent in the general population presenting with ectopic pregnancy 4
Most Common Population-Level Risk (Answer to This Question)
- Pelvic inflammatory disease is the most frequently encountered predisposing factor in clinical practice 4, 5
- PID increases ectopic pregnancy risk 4-fold (OR 4.00; 95% CI: 3.46-4.61) 5
- Risk doubles with each recurrent episode due to progressive tubal occlusion 1, 2
- In one large study, previous pelvic surgery (29.5%), infertility treatment (25%), and PID (22.7%) were the most common predisposing factors identified 4
Why Each Option Matters
Option A: Induction of Ovulation
- Assisted reproductive technology has become an increasingly important risk factor 1, 2
- However, even with IVF, underlying tubal factors (previous PID, tubal surgery, previous ectopic) remain the most important underlying risk factors 1, 2
- This is a contributing factor but not the primary driver 6
Option B: Previous Tubal Pregnancy
- Creates the strongest individual risk with 10-20% recurrence rate 3, 7
- Previous ectopic pregnancy showed OR 9.03 (95% CI: 7.18-11.35) in meta-analysis 5
- However, this is less common as a presenting risk factor since most patients have not had a prior ectopic 4
Option C: Pelvic Inflammatory Disease (CORRECT ANSWER)
- Most frequently identified predisposing factor in clinical practice 4
- Accounts for approximately 22.7% of ectopic pregnancy cases 4
- OR 4.00 (95% CI: 3.46-4.61) for ectopic pregnancy occurrence 5
- Many women with tubal factor infertility do not report history of salpingitis due to non-specific or absent symptoms, making the true prevalence even higher 2
Option D: Intrauterine Device Use
- Shows only slightly increased risk in meta-analysis 5
- Not among the major predisposing factors identified in clinical studies 4
Critical Clinical Pitfall
The most important caveat: While previous ectopic pregnancy and tubal surgery carry the highest individual risk, PID is the most common predisposing factor encountered in clinical practice because it affects a much larger population and often goes undiagnosed due to asymptomatic chlamydia infection 2, 4. Approximately 17% of women treated for PID will become infertile, and 10% who become pregnant after PID will experience ectopic pregnancy 2.