What Causes a False Positive Fern Test

Well-estrogenized cervical mucus or a fingerprint on the microscope slide may cause a false-positive fern test; false negatives can be due to inadequate amniotic fluid on the swab or heavy contamination with vaginal discharge or blood.

How accurate is Fern test?

Additionally, the accuracy of ferning is markedly less in women who are not in labor as compared to those in labor, with a reported sensitivity and specificity of 51% and 70%, respectively, in patients without labor and 98% and 88%, respectively, in patients in labor.

Can you get a false positive amniotic fluid test?

More recent studies have stated the sensitivity to be 78.1%, compared to 95.7% sensitivity of the Amnisure test. Amnisure does have a high false positive rate, noted to be 19-30% in patients who were later found to have intact membranes by clinical measures, including negative pooling, arborization, and nitrizine.