Fern Test

One of the ways providers used to see if a patient had ruptured membranes (broken water) was to utilize a method called “Ferning.”

It is a diagnostic test where amniotic fluid is placed on a microscope slide and if it dries in a “fern pattern,” the patient is considered to have ruptured membranes.

Some of the limitations of the test include debris or blood in the sample, causing a false negative. “Ferning” can also be seen in other types of bodily fluids, causing a false positive. Prolonged rupture of membranes (greater than 24 hours) or slow, minimal leaks can cause false negative results. Because of these false positives and negatives, many providers have moved away from ferning. Nitrazine paper was also used to determine rupture of membranes since amniotic fluid has a higher pH but again, it can create false positives due to contamination.

Ok, so what do providers use?

Great question! The standard is now to use a point of care biochemical test like Amnisure(R) PAMG-1, in which the provider places a sterile swab for one minute, swab in the solvent for one minute then sent to the lab. Results can be available within 5-10 minutes (although lab variances do occur!). This test has a 98.9% sensitivity and 98.1% specificity rate, meaning it has much lower false positive/negative rate, making it the preferred test.

As always, if there are any questions, do not hesitiate to ask your provider.