Correlation between thromboplastic activity and lecithin/sphingomyelin ratio in amniotic fluid preliminary report.

THe thromboplastic activity of amniotic fluid was correlated with the lecithin sphingomyelin (L/S) ratio in 59 pregnancies. It was shown that the thromboplastic activity and the L/S ratio in amniotic fluid had a coefficient of correlation of r = --0-73 (P less than 0-004). The thromboplastic activity was estimated by a modified method for prothrombin time, and a time of 113 seconds appeared to correspond to an L/S ratio of 2, in that it was the border line between maturity and immaturity of the fetal lungs. Thirty women were delivered within 24 hours of a sample of amniotic fluid being obtained. In the three patients whose babies developed the respiratory distress syndrome, the thromboplastic activity was estimated as being slower than 113 seconds.