Clinical meaning
The amniotic membranes (amnion and chorion) form a fluid-filled sac that protects the fetus throughout pregnancy. Amniotic fluid has an alkaline pH (7.0-7.5) compared to acidic vaginal secretions (3.5-4.5), which forms the basis of the nitrazine test. Rupture of membranes (ROM) can be spontaneous during labor (SROM), premature before labor at term (PROM), or preterm before 37 weeks (PPROM). PPROM is an obstetric emergency due to simultaneous risks of prematurity, infection (chorioamnionitis), and cord prolapse.
Exam relevance
Risk factors: - History of previous PROM or PPROM - Genital tract infections (bacterial vaginosis, GBS, chlamydia) - Polyhydramnios - Multiple gestation - Cervical insufficiency - Cigarette smoking during pregnancy - Low socioeconomic status and inadequate prenatal care
Diagnostics: - Nitrazine test: blue = positive (alkaline amniotic fluid pH 7.0-7.5) - Ferning test: crystalline fern pattern on air-dried slide confirms amniotic fluid - Sterile speculum exam: visualize fluid pooling in posterior fornix - AmniSure test (PAMG-1): highly sensitive and specific for amniotic fluid - Ultrasound for amniotic fluid index (oligohydramnios supports ROM diagnosis) - GBS vaginal-rectal culture if status unknown