Amniotic fluid shake test versus lecithin-sphingomyelin ratio in the antenatal prediction of respiratory distress syndrome.

Surfactant content of 211 amniotic fluid samples raken between 28 and 42 weeks' gestations was determined by the shake test. Parallel with this also the lecithin/sphingomyelin (L/S) ratio was measured in 99 cases. When the test was positive no respiratory distress syndrome (RDS) occurred, while 25 RDS (53.34%) developed in 46 newborns with negative test and 8 RDS (15.38%) in 52 newborns with intermediate test. RDS was observed in all cases when the L/S ratio was below 1.5. At L/S ratios between 1.5 and 2.0, RDS appeared in 50% of the negative tests and 20% of the intermediate tests. However, when the L/S ratio was over 2.0 no RDS occured even in the case of negative tests. For the clinical praxis the positive test gives an exact information; no RDS is to be expected in such cases. In the case of a negative test, however, the authors think is necessary also to determine the L/S ratio.