The prediction of fetal lung maturity from the surface tension characteristics of amniotic fluid.

In recent years fetal lung maturity has been assessed by chemical determination of lung surfactant components in the amniotic fluid. The variation in the results, however, limits the clinical usefulness of these methods. To establish reliable criteria for fetal lung maturity 98 specimens of amniotic fluid were obtained in the 23rd to 41st week of gestation and their surface properties measured in the surface balance (Fig 1). A continuous rise in surface activity of amniotic fluid was observed during this period (Fig. 2). In the evaluation of the surface activity of amniotic fluid y-min appears to be the most suitable parameter because it shows a considerable change during the course of pregnancy and has low variations (Fig. 3). In 64 prematures amniotic fluid was obtained during delivery and its surface properties measured. The correlation of clinical symptoms of the premature with y-min of the amniotic fluid makes it possible to predict the fetal lung maturity at a given y-min value (Fig. 4). When the results are arranged according to the incidence of RDS (lethal RDS, recovered from RDS and without RDS) three y-min-ranges can be clearly distinguished. When y-min of the amniotic fluid is over 27 dyn/cm the probability of lethal RDS is 100%, whereas when y-min is under 17 dyn/cm a mature lung can be expected. In the range between 27 to 17 dyn/cm any degree of lung maturity can be encountered. By division of this range in two additional ones a more accurate prediction of fetal lung maturity is possible: In the y-min-range 27-23 dyn/cm RDS-probability is approximately 70%, in the range 23-17 dyn/cm it is only 30% (Fig. 4). Measurements of surface activity of the amniotic fluid make it possible to predict fetal lung maturity and estimate RDS-probability.