Provider performed microscopy. The fern test is based on the ability of amniotic fluid to form a microscopic crystalline pattern that resembles fern leaves when the fluid air dries on a glass slide.
Performed by authorized providers in the point of care. Used to assess for premature amniotic fluid leakage: i.e. PROM (Premature Rupture of Membranes) or PPROM (Preterm Premature Rupture of Membranes).
•Cellar debris and blood in the sample may inhibit crystallization of amniotic fluid, and cause a false negative.
•"Ferning" is not specific for amniotic fluid. Other fluids (e.g., blood cervical mucus, semen and some urine specimens) when dried can also yield microscopic crystallizations in a "fern" pattern, and cause false positives.
•Prolonged rupture of membranes (greater than 24 hours) or slow, minimal leaks can yield false negative results.
1. A sterile speculum is placed into the vagina. A lubricant or antiseptic should not be used as these substances will affect ferning.
2. Using a sterile cotton swab, obtain sample of vaginal secretions from the posterior vagina where fluid has pooled. Do not touch the mucus plug on cervix.
For more test specific information, please refer to the test procedure found on the Michigan Medicine POC website: https://www.pathology.med.umich.edu/point-of-care