Surface properties of the amniotic fluid in normal pregnancy.

The surface properties of the amniotic fluid were determined in 96 normal pregnancies between weeks 23 and 41. The y-max, y-min, hysteresis areaa, and stability index were used as parameters for evaluation of the surface tension are diagrams. These results were plotted against the gestation week and a curve for the normal course of surface tension of the amniotic fluid during the second half of gestation was obtained. The influence of addition of blood, vernix, and meconium to amniotic fluid as well as that of changes in the pH and dilution were examined. The results were unaffected by either blood, vernix, or pH changes. The slight scatter of the y-min values makes this parameter particularly suitable for determining fetal lung maturity.