[Relation between procoagulant activity and fetal lung maturity in amniotic fluid]

A total of 146 samples of amniotic fluid from the 15th to 43rd weeks of pregnancy were taken by either transabdominal amniocentesis or amniotomy during birth. In addition to the palmitic/stearic ratio (P/S) the following coagulation tests were determined: clotting time, modified prothrombin time, partial thromboplastin time (PTT), recalcification time and, in selected samples, thrombelastograms. In the course of pregnancy there is a significant shortening of all coagulation tests measured in amniotic fluid. Comparing the values obtained in the 15th to 18th and the 37th to 43rd weeks of gestation and literature results the following values may indicate fetal maturity: clotting time less than 100 sec., modified prothrombin time less than 80 sec., PTT less than 30 sec. and recalcification time less than 80 sec. The lower limit for P/S ratio in normal pregnancy is 5,0. In 58 cases, amniotic fluid was obtained in the 37th to 43rd week at most 24 hours before delivery; there was no case of RDS in this group. Eliminating intermediate P/S values of 4,5 to 5,0 a false negative rate of 1,7% for the prediction of fetal lung maturity was seen. The corresponding rate for the modified prothrombin time was 3,4% and for the clotting time 6,4%. In 7 RDS cases all cases could be properly predicted from the recalcification time and the PTT. The fetal lung maturity may be estimated by means of simple and rapid coagulation tests and this may facilitate the indication for RDS-prophylaxis. The determination of the L/S or P/S ratios, however, cannot yet be dispensed with.