Reevaluation of the pH, ferning and nile blue sulphate staining methods in pregnant women with premature rupture of the fetal membranes.

The accuracy rates of 3 diagnostic methods, namely pH determination, fern test and nile blue sulphate (NBS) staining, in the evaluation of women with prolonged premature rupture of fetal membranes (PRM), were investigated in a prospective study. Two hundred and sixty-two women, divided into control and test groups, were examined. A total of 1725 tests were performed. The results indicate that these tests have high inaccuracy rates which increase progressively when more than one hour has elapsed since the rupture of the membranes, and become unreliable after 24 hours. It is concluded that in cases of prolonged PRM these tests provide no better diagnostic information than that obtained by clinical evaluation.