A reevaluation of the ferning test to detect ruptured membranes

The ferning test for the detection of amniotic fluid, when first described, was reported to have no false positive results. Despite this and after initial enthusiasm it has never achieved widespread use. The test is easy to perform but interpretation requires care, and it is necessary to identify potentially confusing crystallization patterns to avoid false positive results. A reevaluation of the test is presented and a hitherto unrecognized false positive reaction due to an antiseptic solution is reported.