Performance of the amniotic fluid foam stability—50 percent test: A bedside precedure for the prenatal detection of hyaline membrane disease

Abstract

A study was conducted on 394 patients in order to evaluate a modified foam stability (FS) test for the prenatal evaluation of fetal oulmonary maturity. We termed the assay the “FS-50 test” because of its dependence upon the maintenance of a 50% ethanol concentration in the final assay mixture. The FS-50 test was regarded as “positive” when an uninterrupted ring of stable bubbles formed around the meniscus of the tube at the air-fluid interface, following vigorous shaking. Anything less was regarded as a “negative” result. Neonatal hyaline membrane disease (HMD) did not occur in association with a “positive” FS-50 test result. However, when the FS-50 test was “negative,” 35.8% of the neonates developed HMD. In 164 of the 394 patients studied, sufficient amniotic fluid was available so as to enable us to perform the FS-50 and the lecithin/sphingomyelin (LS) ratio assay concurrently. LS ratio values of greater than 2.0 correctly predicted a sufficient degree of fetal pulmonary maturity so as to protect against the subsequent development of HMD in 97.8% of the cases. LS ratio values of less than 2.0 were predictive of HMD in 28.4% of the cases studied, while a “negative” FS-50 test correctly predicted that HMD would subsequently occur in 46.9% of the cases. The FS-50 test promises to provide a reliable screening method for the prenatal detection of HMD. The practicability and sensitivity of this simple assay makes it a potentially valuable addition to our diagnostic armamentarium.