What is the accuracy of the Rupture of Membranes (ROM) test for diagnosing ruptured membranes in pregnant women?

Accuracy of ROM Testing for Ruptured Membranes

Modern point-of-care immunoassay tests for rupture of membranes demonstrate excellent diagnostic accuracy, with sensitivities of 89-100% and specificities of 95-100%, substantially outperforming traditional methods like the fern test. 1, 2

Diagnostic Performance of Available Tests

Immunoassay Tests (Preferred Method)

Monoclonal/polyclonal immunoassay tests (ROM Plus®) provide the highest diagnostic accuracy:

• Sensitivity: 96-100% 1, 2
• Specificity: 95-99% 1, 2
• Positive predictive value: 75-96% 1, 2
• Negative predictive value: 99-100% 1, 2
• Overall accuracy: 95-98% 1, 2

PAMG-1 (Placental Alpha-Microglobulin-1) immunoassay tests (AmniSure®) show similar performance:

• Sensitivity: 89-97% 2, 3
• Specificity: 69-100% 2, 3
• Positive predictive value: 91-100% 2, 3
• Negative predictive value: 91-97% 2, 3
• Overall accuracy: 89-97% 2, 3

Traditional Methods (Lower Accuracy)

The fern test demonstrates significantly inferior performance:

• Sensitivity: 78-89% 1, 4
• Specificity: 79% 1
• Positive predictive value: 37% 1
• Negative predictive value: 96% 1
• Overall accuracy: 79-89% 1, 4

Vaginal pH/nitrazine testing shows limited reliability:

• Sensitivity: 73-91% 5
• Specificity: 72-87% 5, 4
• Overall accuracy: 87% 4

Improved AFP (alpha-fetoprotein) testing:

• Sensitivity: significantly higher than nitrazine (P < 0.05) 4
• Specificity: not separately reported 4
• Overall accuracy: 96% 4
• Reaction time: 90 seconds 4

Performance by Gestational Age

For preterm patients (<37 weeks), both ROM Plus® and AmniSure® achieve 100% diagnostic accuracy with perfect concordance to clinical confirmation. 2

For term patients (≥37 weeks):

• ROM Plus® sensitivity: 94%, specificity: 97% 2
• AmniSure® sensitivity: 81%, specificity: 100% 2

Clinical Implications

Accurate ROM diagnosis is critical because:

• The risk of infection increases significantly after 18 hours of membrane rupture 6
• In previable PPROM (<24 weeks), intraamniotic infection occurs in 38% with expectant management 7, 6
• Maternal sepsis occurs in up to 6.8% of previable/periviable PPROM cases 7
• Timely diagnosis allows for gestational age-specific interventions to optimize perinatal outcomes 1, 2

Key Diagnostic Pitfalls to Avoid

False positives can occur with immunoassays due to:

• Blood contamination (though modern tests are designed to minimize this) 5
• Semen exposure 5

False negatives with traditional methods occur due to:

• Insufficient amniotic fluid sample 5
• Delayed testing after initial fluid leakage 5
• Blood or vaginal discharge interference with pH testing 5

The fern test is particularly unreliable, with only 37% positive predictive value, meaning most positive results are false positives. 1

Recommended Testing Algorithm

When ROM is suspected based on patient history of fluid leakage:

1. Perform speculum examination to visualize fluid pooling or leakage from cervical os 7, 6
2. If visualization is inconclusive, use point-of-care immunoassay testing (ROM Plus® or AmniSure®) as first-line diagnostic test 1, 2
3. Avoid digital cervical examination until ROM is confirmed to minimize infection risk 8
4. Do not rely on fern test or nitrazine test alone due to inferior accuracy 1

After ROM confirmation, immediately assess for signs of infection: maternal fever ≥100.4°F (≥38.0°C), maternal tachycardia, purulent cervical discharge, fetal tachycardia, or uterine tenderness, as infection may present without fever especially at earlier gestational ages. 7, 6