The amniotic fluid foam test, L/S ratio, and total phospholipids in the evaluation of fetal lung maturity

The results of the L/S ratio, TPL (total phospholipids) concentration, and the FT (foam test) from 126 amniotic fluid samples (105 of which were obtained less than 48 hours before delivery) between weeks 26 and 43 of gestation were compared in evaluating fetal lung maturity. A perfect correlation between an L/S ratio of 2 or more and TPL of 2.8 mg./100 ml. or more and pulmonary maturity was found. L/S ratio of 1.4 or less and TPL of 1.5 mg./100 ml. or less were associated in all cases with RDS. The intermediate zone between these values, where pulmonary maturity could not be predicted, contained 3.8 per cent of the cases when L/S ratio is evaluated compared to 21.9 per cent by TPL assessment. The intermediate and positive FT were associated in all cases with fetal lung maturity and mature values of L/S ratio and TPL; the negative FT cases (36 out of 105) were associated with a wide range of TPL and L/S ratio values including immature, intermediate, and mature values. No RDS occurred in cases in which the FT was positive or intermediate. It is concluded that the FT is highly valuable as a screening test. If positive or intermediate, the risk of RDS is very small; when negative, the sample should be subjected to chemical analysis.