Measuring the number of lamellar body particles in amniotic fluid

We describe a method for determining the number and size distribution of lamellar bodies and compare the results prospectively with other tests for fetal lung maturity: lecithin-sphingomyelin ratio (L/S), phosphatidylglycerol, and fluorescence polarization. The technique uses an electronic particle counter calibrated for a size range of 1.7-7.3 fL. The number of lamellar bodies in amniotic fluid samples varied from 3800-166,000 particles per microliter and correlated strongly with L/S ratio (r = 0.75; N = 144) and fluorescence polarization (r = -0.78; N = 165). Amniotic fluid samples stored for up to 10 days at 4C had stable lamellar body counts (within +/- 11%). Longer storage tended to decrease the counts. Addition of more than 1% (v/v) whole blood significantly decreased the lamellar body counts. This technique shows promise for the rapid assessment of fetal lung maturity.