Principle: | Clinical Significance: | Specimen/Specimen Acquisition: | Materials: | Reagents: | Standardization: N.A. | Procedure: | Limitations: | Expected Result(s) | Quality Control: | Addendum; Microscope | References:
The “Fern” test is based upon the ability of amniotic fluid to form a microscopic crystalline pattern suggestive of fern leaves when the fluid specimen is allowed to air dry on a glass slide; the phenomenon is due to the interaction of high concentrations of electrolytes and protein in amniotic fluid relative to other fluids that may be present in the posterior vagina.
The procedure is performed by a physician or nurse midwife who has completed the competency validation described in this procedure.
The procedure allows for the qualitative assessment/detection of premature amniotic fluid leakage; i.e., PROM (Premature Rupture of Membranes).
The Fern test is often run in conjunction with the Nitrazine test to confirm or rule out the presence of amniotic fluid.
1. A vaginal swab obtained from the posterior vaginal pool. As when handling any bodily fluid, Universal Precautions must be observed.
2. Position the patient in the dorsal lithotomy position.
3. Avoiding the use of lubricant or antiseptic, place a sterile speculum into the vaginal vault.
4. Using a sterile cotton swab, obtain a sample of the vaginal secretion from the posterior vaginal pool.
5. Smear a thin layer of the fluid obtained on the center portion of a clean glass microscope slide.
6. Allow the slide to air dry for at least 5 – 7 minutes. Do not wave or blow on the slide and do not apply heat to assist in drying.
1. Sterile vaginal speculum.
2. Sterile cotton-tipped swab
4. Lens cleaner (provided by the laboratory)
5. Lens tissue (provided by the laboratory)
6. Clean microscope slides
8. Biohazard container
1. No reagents are required for this testing procedure.
1. When the slide has completely air dried (at least 5 to 7 minutes), place it on the stage of the light microscope provided for the procedure.
2. Examine the slide under low power (10X).
3. Look for fern-like crystals. If positive for amniotic fluid, this crystal formation will be present in most microscopic fields.
Negative for crystal ferning
Positive for crystal ferning
4. Record results in the patient’s chart as either “Fern test positive for amniotic fluid” or, in the absence of the characteristic fern-like crystals “Fern test negative for amniotic fluid”.
Contamination with blood, urine or cervical mucus may result in false positives.
NA. The test is run based entirely on clinical presentation and must be interpreted in light of the clinical situation.
1. The test is a PPMP (Provider Performed Microscopy Procedure) as defined by certifying agencies; “waived” testing standards do not apply. It requires demonstration of competency by individuals performing it.
In this case it’s a matter of recognizing the ferning crystallization pattern characteristic of dried amniotic fluid. Numbered photomicrographs (example) will be circulated, initially twice per year and then once every following year, to those authorized to perform the test. These individuals will identify both positive and negative images relative to “ferning” and return the photomicrograph forms to the laboratory for documentation. Participants should be able to identify ferning or lack of it on all five of the challenges. If an individual has a problem with any of the photomicrographs, the UCL Technical Director will inform a pathologist at that site who will arrange to go over the images with the practitioner. This follow-up effort will be documented, scanned and indexed into the record.
Care and maintenance of the microscopes provided for Fern Testing is important but also quite simple.
1. The microscope needs to be covered when not in use primarily to protect the objectives and oculars from dust accumulation.
2. Clean the objective lens following each use with the lens cleaner and lens paper provided. Note: Do not use a dry cloth, “Kleenex” or gauze when cleaning the oculars; this will generally scratch the sensitive glass surfaces.
3. The 10X objective must be kept free from oil at all times.
4. The microscopes for Fern Testing will be formally inspected, cleaned and aligned once per year and by special request from Nursing Service by the laboratory Instrument Specialists. A Maintenance, Function-Verification report will be issued.
1. “Amniotic Fluid Fern Testing”; Family Birthing Suites – the Finley Hospital, 20040515
2. S. Raymond; United Clinical Laboratories Technical Director/CIO
3. January 1, 2007 (HR.3.10 in the Comprehensive Accreditation Manual for Laboratory and Point-of-Care Testing)
i. March 2008; S.Raymond
July 2010 L. McGovern (no changes)
September 2011 L. McGovern (no changes)
October 2011 L. McGovern (Revised: discontinued log)