Evaluation of fetal pulmonary maturity by gas-chromatographic analysis of amniotic fluid palmitic acid/stearic acid (P/S) ratio.

Gas-chromatographic analysis of the fatty acids (P/S ratio) in 212 samples of amniotic fluid, 35 samples of vernix caseosa and 35 samples of the pellets obtained after centrifugation of the amniotic fluid were carried out to evaluate the effects of contaminants that might be present in amniotic fluid on the P/S ratio. The P/S ratio is used as an index of the degree of maturity of the fetal or neonatal lungs. Analysis of variance applied to the means of the P/S values for each of above materials showed them to be significantly different and attests to the importance of centrifugation for obtaining valid results. We propose a standard procedure of centrifugation for 60 minutes at 3500 X g followed by extraction and gas-chromatography as a rapid, valid way to measure the P/S ratio.