Fern test

A diagnostic test used in obstetrics

Fern test

The fern test is a diagnostic procedure used primarily in the field of obstetrics to detect the presence of amniotic fluid, which can indicate rupture of membranes (ROM) during pregnancy. This test is named for the characteristic "fern-like" pattern that amniotic fluid forms when it dries on a microscope slide.

Procedure

The fern test is performed by collecting a sample of vaginal fluid using a sterile speculum and a swab. The collected fluid is then spread thinly on a clean microscope slide and allowed to air dry. Once dried, the slide is examined under a microscope.

A positive fern test showing the characteristic fern-like pattern.

Interpretation

A positive fern test is indicated by the presence of a crystalline pattern resembling fern leaves. This pattern is due to the high sodium chloride content in amniotic fluid, which crystallizes in a distinctive manner. A positive result suggests that the membranes have ruptured, allowing amniotic fluid to leak into the vaginal canal.

A negative fern test, on the other hand, shows no such pattern and may indicate that the fluid is not amniotic in origin, or that the membranes are still intact.

Clinical significance

The fern test is a valuable tool in the assessment of suspected premature rupture of membranes (PROM), a condition that can lead to complications such as preterm birth and infection. Accurate diagnosis is crucial for the management and treatment of PROM to ensure the health and safety of both the mother and the fetus.

Limitations

While the fern test is a useful diagnostic tool, it is not infallible. False positives can occur if other fluids, such as cervical mucus, are present, as they can sometimes mimic the fern pattern. False negatives may occur if the sample is not collected properly or if the slide is not allowed to dry completely.

Related pages

• Amniotic fluid
• Premature rupture of membranes
• Obstetrics
• Pregnancy