Rupture of Membranes Evaluation
Radhika Patnam, MD
Clinical Scenario A
A 26 y/o G1 female @ 37.5 weeks gestation presented to the hospital exam room after noticing her “underwear was wet.” She denied any contractions or bleeding, and endorsed good fetal movement. Her NST was reactive and no contractions were noted. A speculum was placed, and showed no pool of fluid. Nitrazine testing was negative and no arborization was noted on the slide. The final assessment was that spontaneous rupture of membranes had not occurred and the patient was sent home after 25 minutes with labor precautions.
Clinical Scenario B
A 26 y/o G1 female @ 37.5 weeks gestation presented to the hospital exam room after noticing her “underwear was wet.” She denied any contractions or bleeding, and endorsed good fetal movement. Her NST was reactive and no contractions were noted. An Amnisure was inserted per manufacturer’s instructions. The test returned after 45 minutes with a negative result. The final assessment was that spontaneous rupture of membranes had not occurred and the patient was sent home with labor precautions.
- Which test is technically more accurate, traditional speculum exam or Amnisure for rupture of membranes?
- When should an Amnisure be used?
Costs Scenario A
Hospital Exam Room visit: Level III physician visit, $278.00*|
NST: $150.00 physician reading fee* + $395.00 facility fee*
Speculum exam and nitrazine testing: no lab charge
Total Charges: $823.00
Hospital Exam Room visit: Level III physician visit, $278*
NST: $150 physician reading fee* + $395 facility fee*
Total Charges: $1336.00
Cost difference: $513.00
*Amount charged by billing department at Medical University of South Carolina to insurance company.
Amnisure has been extensively studied, and is a great tool to detect rupture of membranes. Multiple studies have shown sensitivity of 99%, with high positive and negative predictive values. Comparatively, each individual test of the traditional speculum exam is not as sensitive or specific, with false testing from infections, mucous, semen and timing since rupture. Arborization has a false positive rate of 5-30%, and nitrizine has a false positive rate 17.4%. The combination of arborization, nitrizine and history was originally investigated in the 1960s, and found to have a diagnostic accuracy of 93.1%. More recent studies have stated the sensitivity to be 78.1%, compared to 95.7% sensitivity of the Amnisure test. Amnisure does have a high false positive rate, noted to be 19-30% in patients who were later found to have intact membranes by clinical measures, including negative pooling, arborization, and nitrizine. The Amnisure test has been shown to be more sensitive, but this must be weighed against the significant expense of its testing and false positive rate. In scenarios where testing is equivocal, for example when a patient has positive nitrizine testing with pooling but without arborization, Amnisure can play an important role to diagnose rupture of membranes. However, given its prohibitive cost, per ACOG guidelines, it should not be used as the primary method to diagnose rupture of membranes.
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- Lee, Si Eun, et al. "Measurement of placental alpha-microglobulin-1 in cervicovaginal discharge to diagnose rupture of membranes." Obstetrics & Gynecology 109.3 (2007): 634-640.
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- Ng, Beng Kwang, et al. "Comparison between AmniSure placental alpha microglobulin-1 rapid immunoassay and standard diagnostic methods for detection of rupture of membranes." BioMed research international (2013).
- American College of Obstetrics & Gynecology. (2013). ACOG practice bulletin no. 139: Premature Rupture of Membranes. Obstet Gynecol.