A new method for assessment of fetal lung maturity.

A new method for evaluation of fetal lung maturity in utero is described. The method is based on the fluorescence polarization (P) of the lipids in the amniotic fluid after labelling with a special dye. Tests performed with 49 amniotic fluid samples drawn from 33 pregnancies clearly demonstrated a decrease in P during gestation which correlated with the increase in the lecithin/sphingomyelin ratio (L/S) in the fluid. During gestation the P value at 24 degrees C decreased steadily from about 0-4 to 0-2 and the value of P (24 degrees C) = 0-310 has been tentatively chosen as the threshold above which respiratory distress syndrome may develop. The described method, which requires a specially designed instrument, offers a series of important advantages over the presently available methods. It is simple, rapid, highly accurate and reproducible, and independent of amniotic fluid volume. The P value reflects the microviscosity in the whole lipid assembly of amniotic fluid and is not confined specifically to lecithin.