What is the endometriosis fertility index and how does it predict pregnancy outcomes?

Endometriosis Fertility Index (EFI): A Validated Tool for Predicting Pregnancy Outcomes

The Endometriosis Fertility Index (EFI) is a simple, robust, and validated clinical tool that accurately predicts fertility outcomes for women following surgical staging of endometriosis, providing essential guidance for developing treatment plans for infertile women with endometriosis. 1

What is the Endometriosis Fertility Index?

The EFI is a clinical staging system specifically designed to predict pregnancy rates in patients with surgically documented endometriosis who attempt non-IVF conception. Unlike other classification systems for endometriosis, the EFI was developed through comprehensive statistical analysis of actual patient data rather than a priori assumptions 2.

Key components of the EFI include:

• Least Function Score: The most important predictive factor in the EFI system, representing the sum of scores determined intraoperatively after surgical intervention that describe the function of the tube, fimbria, and ovary on both sides 3, 2
• Historical factors: Including age, duration of infertility, and prior pregnancy history
• Surgical findings: Including the revised American Society for Reproductive Medicine (r-ASRM) score and stage

How EFI Compares to Other Classification Systems

The EFI offers significant advantages over other endometriosis classification systems:

• Superior to r-ASRM classification: The EFI has greater predictive power for IVF outcomes in endometriosis patients than the r-ASRM classification, with a significantly larger Area Under the Curve (AUC = 0.641 vs. 0.445) 4
• Validated for all infertile patients: The EFI has demonstrated predictive power for successful pregnancy with natural intercourse or intrauterine insemination in infertile patients, regardless of endometriosis severity 5
• Recommended by expert consensus: The World Endometriosis Society strongly recommends that all women with endometriosis for whom fertility is a future concern should have an EFI score completed and documented in their medical records 1

How EFI Predicts Pregnancy Outcomes

The EFI uses a scoring system from 0-10, with higher scores indicating better prognosis:

• EFI ≥ 7: Associated with higher spontaneous pregnancy rates (75% of spontaneous pregnancies occur in patients with EFI ≥ 7) 6
• EFI ≥ 6: Patients with scores ≥ 6 show significantly higher implantation rates, clinical pregnancy rates, and cumulative pregnancy rates compared to those with scores ≤ 5 4
• EFI 2-4 vs. 6-9: The overall live birth rate for patients with low EFI scores (2-4) is only 17% compared with 83.8% for those with higher EFI scores (6-9) 6

Clinical Application Algorithm

1. Calculate EFI score after surgical staging of endometriosis

   • Document least function score of tubes, fimbria, and ovaries
   • Include historical factors (age, infertility duration, prior pregnancy)
   • Calculate final EFI score (0-10)

2. Treatment recommendations based on EFI score:

   • EFI ≥ 7: Recommend attempting natural conception for up to 12 months
   • EFI 5-6: Consider attempting natural conception for 6-12 months before moving to assisted reproduction
   • EFI ≤ 4: Consider immediate referral for assisted reproductive technologies

3. Timing considerations:

   • Most spontaneous pregnancies (82.7%) occur within the first 12 months after surgery 6
   • For patients with EFI ≥ 5 who haven't conceived after 12 months post-surgery, IVF-ET is recommended to achieve higher pregnancy rates 3

Important Clinical Considerations

• Predictive factors: Younger age, shorter duration of infertility, and higher EFI scores are positively associated with successful pregnancy without ART after laparoscopic surgery 5
• Risk factors for low EFI: Infertility duration ≥36 months and presence of endometrioma increase the probability of having EFI ≤ 5 6
• IVF outcomes: The EFI score also correlates with IVF parameters including antral follicle count, estradiol levels, number of oocytes retrieved, fertilization rates, and embryo quality 4

Pitfalls and Caveats

• The EFI requires surgical staging of endometriosis, limiting its use in patients diagnosed non-surgically
• While highly predictive, the EFI should be calculated immediately after surgical intervention when the functional status of reproductive organs can be accurately assessed
• The EFI was designed primarily for non-IVF conception prediction, though studies show it also has value in predicting IVF outcomes
• Regular reassessment of fertility plans is necessary, as most spontaneous pregnancies occur within 12 months of surgery, after which assisted reproduction should be considered

By providing objective, evidence-based predictions of fertility outcomes, the EFI helps clinicians and patients make informed decisions about fertility treatment approaches, potentially avoiding unnecessary treatments for those with good prognoses and preventing wasted time for those with poor prognoses.