Fern test
Fern test refers to 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 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. It also may provide indirect evidence of ovulation and fertility, although it does not predict the time of ovulation.
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Ferning occurs due to the presence of sodium chloride in mucus under estrogen effect. When high levels of estrogen are present, just before ovulation, the cervical mucus forms fern-like patterns due to crystallization of sodium chloride on mucus fibers. This pattern is known as arborization or 'ferning'.[1]
When progesterone is the dominant hormone, as it would be in the second half of a normal cycle, the fern pattern is no longer discernible, and the pattern is completely absent by the 22nd day of a woman's cycle. The disappearance of the fern pattern after the 22nd day suggests ovulation, and its persistence throughout the menstrual cycle may suggest an anovulatory cycle.[1]
References
- Patrick Duff, MD (2016). Preterm premature (prelabor) rupture of membranes. In Vanessa A Barss, MD, FACOG (Ed.), uptodate Retrieved from http://www.uptodate.com/'