The thromboplastic activity of lung surfactant in amniotic fluid and its application to prenatal assessment of fetal lung maturity.

Based on the fact that both tissue thromboplastin and lung surfactant show lamellar structures under the electron microscope and belong chemically to lipoprotein, the thromboplastic activity of lung surfactant in amniotic fluid was studied by measuring plasma recalcification time. The results obtained were as follows (1) The surfactant fractions isolated from amniotic fluid and rabbit or pig lung showed the thromboplastic activity with dose response. (2) The thromboplastic activity of amniotic fluid increased with advancing gestational age. (3) It was found that the thromboplastic activity determined by plasma recalcification time was parallel with the surfactant concentration of amniotic fluid. (4) The shortening rate of plasma recalcification time in amniotic fluid could estimate well the risk of RDS, and the critical value for RDS was assumed to be about 33%.