Objective: To compare the accuracy of an immunoassay to measure levels of placental alpha-microglobulin-1 in cervicovaginal secretions with that of conventional clinical assessment for the diagnosis of rupture of membranes.
Methods: A prospective observational study was performed in consecutive patients with signs or symptoms of rupture of membranes at Seoul National University Hospital from March 2005 to February 2006. Initial evaluation included both the standard clinical evaluation for rupture of membranes and placental alpha-microglobulin-1 immunoassay. Rupture of membranes was diagnosed if fluid was seen leaking from the cervical os or if two of the following three conditions were present: pooling of fluid, positive nitrazine test, or ferning. Rupture of membranes was diagnosed definitively on review of the medical records after delivery.
Results: Of 184 patients (11-42 weeks of gestation), rupture of membranes was diagnosed at initial presentation in 76% (139 of 184) using conventional clinical assessment and 88% (161 of 184) using placental alpha-microglobulin-1 immunoassay. Follow-up confirmed that a total of 159 of 183 patients (87%) had rupture of membranes at their initial presentations. Using this longitudinal assessment as the clinical gold standard, placental alpha-microglobulin-1 immunoassay confirmed rupture of membranes at initial presentation with a sensitivity of 98.7% (157 of 159), specificity of 87.5% (21 of 24), positive predictive value of 98.1% (157 of 160), and negative predictive value of 91.3% (21 of 23). Placental alpha-microglobulin-1 immunoassay was better than both the conventional clinical assessment and the nitrazine test alone in confirming the diagnosis of rupture of membranes.
Conclusion: Measurement of placental alpha-microglobulin-1 in cervicovaginal secretions is superior to conventional clinical assessment in the diagnosis of rupture of membranes.
Level of evidence: II.