Fern test

The name refers to the detection of a characteristic "fern like" pattern of vaginal secretions when a specimen is allowed to dry on a glass slide and is viewed under a low-power microscope.

The fern test is most commonly used to provide evidence of the presence of amniotic fluid and is used in obstetrics to detect preterm premature rupture of membranes and/or the onset of labor.

[1] Ferning was first described in the field of gynecology in 1945 by Georgios Papanikolaou, inventor of the pap smear, as a test for ovulation during a normal menstrual cycle.

The sodium chloride content of amniotic fluid secreted by the fetal kidneys may be indicative that membrane rupture has occurred, though the pattern of 'ferning' seen in amniotic fluid is distinct from that seen in cervical mucus.

[1] False positive results are mostly attributable to cervical mucus, though have been reported due to semen and fingerprints, while false negatives are attributable to inadequate fluid available at the time of specimen collection, or contamination from leukorrhea, blood or meconium.