Evaluation of a modified foam stability (FS-50) test. An assay performed on amniotic fluid to predict fetal pulmonary maturity.

Abstract

The authors evaluated a modification proposed by Edwards and Baillie of the original amniotic fluid shake test described by Clements and associates. This foam stability (FS) test involves the use of 100% (v/v) rather than 95% (v/v) ethanol to produce an ethanol volume fraction of 50%, and it is accordingly referred to as the FS-50 test. The tube is shaken and examined for the presence of stable foam. A detailed study in which the results of the FS-50 test were evaluated with respect to neonatal clinical outcome in 104 obstetric cases (60% of the cases were complicated) is presented. In the 80 cases in which the FS-50 test was positive (presence of stable foam), there was no neonate with hyaline membrane disease. In the 24 cases in which FS-50 results were negative (absence of stable foam), 58% of the infants had respiratory problems in the neonatal period, i.e ., eight had hyaline membrane disease and six, transient tachypnea of the newborn. In 77 cases, lecithin/sphingomyelin ratio and the FS-50 test were compared with respect to their relative abilities accurately to predict the fetal pulmonary status. In situations in which the FS-50 test and the lecithin/sphingomyelin ratio results differed, the FS-50 test was found to be more reliable than the lecithin/sphingomyelin ratio. In most of these cases, pregnancies were complicated by diabetes mellitus, intrauterine growth retardation, or chronic hypertension. It is concluded that the FS-50 test is a simple, inexpensive and reliable predictive test of functional surfactant activity, which can rapidly provide critical information to the clinician.