The use of amniotic fluid viscosity measurements to establish fetal lung maturity.

A Haake viscosimeter was used to determine the viscosity of amniotic fluid and this value correlated with fetal lung maturity. The results were evaluated along the weeks of pregnancy and compared to those obtained using Gluck's method (lecithin/sphingomyelin ratio (L/S). Using 91 separate amniotic fluid samples, free of meconium and blood contamination, we found that the new method was quick and easy to perform. Thirty-one neonates were delivered within 48 h of the amniotic fluid sampling and the percentage of correct prediction of respiratory distress syndrome (RDS) was 71% with a mature L/S ratio and 83% with viscosity less than 1.17 cP. In cases with an immature L/S ratio (value below 2) the correct prediction of RDS was 64%; with the fluorescence polarization (FP) technique it was 91%. We conclude that the amniotic fluid FP value is a reliable index of fetal lung maturity and risk for developing RDS and has also specific technical and diagnostic advantages over the L/S ratio.