| Test | How It Is Done | Discussion |
|---|
| Alpha-fetoprotein (AFP) kit | Detects abnormally high concentrations of AFP in vaginal fluids | Sensitivity and specificity are high, about 90–95% |
| Ferning | Assessment of the appearance of dried cervical mucus on a microscope slide. A branching appearance of the dried mucus represents a positive test. | Sensitivity and specificity are only fair (about 60–75%) |
| Fetal fibronectin (fFn) test | Sample cervicovaginal secretions for fFN with a qualitative immunoassay or dipstick indicator | Sensitivity and specificity are high, about 85–95% |
| Intra-amniotic dye injection | Phenol-sulfonphthalein (PSP) or other dye indicators are injected into the amniotic fluid, and assessments are made of the leakage of dye into the vagina. | Sensitivity and specificity are high, but the test is invasive. |
| Nitrazine test | pH indicator test—insert a strip of paper impregnated with nitrazine into the vaginal vault and observe for change in color. | Sensitivity and specificity are only fair (about 60–75%) |
| Ultrasonography | An ultrasound transducer is used transvaginally to determine the length of the cervix. Shorter lengths correlate with an increased risk of premature rupture of membranes. | Sensitivity and specificity are low, esp. in women at low risk for premature delivery. The test is sometimes used in conjunction with other studies. |