Laboratory Tests for the Diagnosis of Rupture of Membranes

BACKGROUND: Rupture of membranes is defined as the leaking of amniotic fluid caused by the breaking of fetal amniotic membranes. Rupture of membranes is a major contributor to neonatal morbidity and mortality because it often occurs at preterm gestational ages leading to preterm birth. It also poses significant risk to maternal and fetal well-being due to the risk of infection, bleeding, cord prolapse, and placental abruption. Diagnosis can be challenging in up to 10% of cases. High diagnostic accuracy is required as it can have a profound impact on the recommendations for management and lead to iatrogenic preterm birth, especially at early gestational ages. CONTENT: Greater than 90% of rupture of membrane diagnoses can be made with physical examination, nitrazine testing, and microscopic fern testing. The gold standard for diagnosis is visualizing clear, amniotic fluid egressing from the external cervical os or with an amniocentesis dye test. The amniocentesis dye test is invasive and is associated with obstetric and fetal risks. Therefore, in cases equivocal for rupture of membrane diagnosis by physical examination, additional commercial immunoassays have been developed to detect protein markers that have a high concentration in amniotic fluid. SUMMARY: Rupture of membrane diagnosis should begin with conventional tests of physical examination, nitrazine paper testing, and microscopic ferning evaluation. Commercial immunoassays should be utilized in equivocal cases to assist in the diagnosis of membrane rupture when the diagnosis is unclear.