A Comparison of Rapid Immunoassay Tests for the Detection of Ruptured Membranes

Premature rupture of membranes (PROM), defined as spontaneous rupture of membranes (ROM) before the onset of uterine contractions, is one of the most common diagnostic dilemmas in contemporary obstetric practice. Premature rupture of membranes can occur at any gestational age, and preterm PROM (PPROM, defined as PROM before 37 weeks) is responsible for 20-40% of preterm births. Early and accurate diagnosis of PROM would allow for gestational age-specific obstetric interventions designed to optimize perinatal outcome and minimize serious complications such as cord prolapse, preterm delivery, fetal distress and infectious morbidity (chorioamnionitis, neonatal sepsis). Conversely, a false-positive diagnosis of PROM may lead to unnecessary obstetric interventions, including hospitalization, administration of antibiotics and corticosteroids, and even induction of labor. Therefore, the correct and timely diagnosis of this disorder is of critical importance to the clinician because PROM and PPROM may be associated with serious maternal and neonatal consequences.

The diagnosis of fetal membrane rupture is conventionally made using a clinical assessment. First, by speculum examination, the clinician looks for amniotic fluid leaking from the cervical os. If clear fluid is visualized leaking from the cervical os, the diagnosis is positive for fetal membrane rupture. More commonly, leaking is absent, and a more extensive workup is required, which includes nitrazine/pH testing, visual inspection of pooling of fluid in the posterior fornix, and a microscopic evaluation of the collected specimen (ferning). Although this approach is considered the standard of care, it is fraught with inaccuracies, requires an intrusive examination and may not provide a rapid diagnosis.

Rapid, point of care, qualitative immunochromatographic tests (ie., Amnisure®, ActimProm®, Amnioquick®) that detect proteins found in amniotic fluid at high concentrations, have been used to diagnose the rupture of membranes (ROM) for several years. In many hospitals, Amnisure® has replaced the sterile speculum exam as the standard of care for diagnosing ROM. It identifies Placental Alpha Microglobulin-1 (PAMG-1), a 34 kd fetal glycoprotein, in cervicovaginal secretions.

Recently a new, rapid, point of care, qualitative immunochromatographic test was introduced to the market, ROM Plus®. Unlike the other immunoassay tests, ROM Plus® uses a unique monoclonal/polyclonal antibody approach to detect two different proteins found in amniotic fluid at high concentrations. ROM Plus® detects Placental Protein-12 (also known as Insulin-like Growth Factor Binding Protein-1) as well as Alpha Fetoprotein (AFP). The combination of PP12 and AFP were chosen not only because of their robust historical literature support as ideal protein markers for amniotic fluid5-22, but also their unique characteristics. PP12 is synthesized by the decidua of the placenta and reaches a very high concentration level in the amniotic fluid early in the first trimester and stays at that level until delivery. However, AFP, synthesized by the fetal liver and yolk sac, reaches its peak concentration late in the second trimester/early third trimester. This increases the chance that the proteins will be detected, especially in the preterm patients, when the diagnosis of ROM is most crucial.

This study is designed to assess the performance (sensitivity, specificity, PPV, NPV) of ROM Plus® and Amnisure®.