The assessment of foetal lung maturity by chemical analysis of amniotic fluid

Advances in the understanding of the neonatal respiratory distress syndrome have led to a proliferation of amniotic fluid tests. Measurement of pulmonary surfactant production is the most direct means of assessing pulmonary maturity. Assays of surfactant are subjected to certain pre-analysis sources of variation, such as variability in amniotic fluid volume, sample collection site, centrifugation speed and time, and contamination with blood and/or meconium. Amniotic fluid surfactant assays can be divided into biochemical and functional tests. When properly performed, both approaches yield results that correlate well with clinical findings. However, no single method has achieved the distinction of total reliability and universal applicability. In most tests the value for mature lungs is almost 99% accurate. On the other hand, immature values have very low accuracy. Therefore, it is advisable to perform an additional test or to repeat the determination. The determination of the lecithin/sphingomyelin ratio is characterized by sufficient accuracy for routine analyses. For scientific studies we recommend the use of a capillary gas-chromatographic method allowing an accurate assessment of dipalmitoylphosphatidylcholine, the most important surfactant constituent.