Effect of gestational variation of phosphatidylglycerol and phosphatidylinositol on the microviscosity of amniotic fluid phospholipids.

Abstract

Amniotic fluid microviscosity, as measured by 1,6-diphenylhexatriene fluorescence polarization, shows an excellent correlation with the most frequently performed test for fetal lung maturity, the Iecithin-sphingomyelin ratio, and is an excellent predictor of respiratory distress syndrome. On the basis of reported percentages of amniotic fluid phospholipids and their variation during gestation, we prepared and measured the microviscosity of phospholipid dispersions with compositions corresponding to amniotic fluid at gestational ages of 35 weeks. Microviscosity of these dispersions decreases with increasing gestational age. Furthermore, physiologic variations in phosphatidyiglycerol and phosphatidylinositol, especially the former, within each gestational period can greatly influence microviscosity values: as either phospholipid was increased in each gestational period, the microviscosity values decreased in a stepwise pattern. Microviscosity measurements are, therefore, sensitive to physiologic variations in all phospholipids important for fetal lung maturity determinations, not just lecithin and sphingomyelin. From this and previous studies we conclude that amniotic fluid fluorescence polarization measurements have diagnostic and technical advantages over the lecithin-sphingomyelin ratio as a test for fetal lung maturity.