The laboratory assessment of fetal lung maturity

The assessment of fetal lung maturity by laboratory methods is reviewed, and the utility of the various approaches in the prediction of respiratory distress syndrome is discussed. Because of the relatively low prevalence of respiratory distress syndrome, methods with exceptionally high diagnostic sensitivity and specificity are required; such methods are rarely available for any diagnostic evaluation, and the methods with the greatest clinical acceptance in assessing fetal lung maturity have been those which require the most personnel time and skill. The consequences of laboratory testing in the environment of low prevalence diseases is discussed. Because of the clinical implications of an erroneous determination of fetal lung maturity, particularly in the case of incorrectly assessing the fetal lungs to be mature, a strong emotional overlay exists for accepting only the "reference method" or "gold standard" in this determination. This review briefly discusses the utility of commonly used methods in the context of the physical and chemical concepts. By reviewing the underlying principles of the methods, the origins of some of the frequently observed problems in this field are revealed. The emphasis is on practical application and issues of use both to clinician and laboratory in approaching this controversial and difficult area of assessment. It is demonstrated that there are several reasonably straightforward approaches which will provide appropriate clinical information more quickly, easily, and inexpensively than the methods generally requested.