The counts appearing in the platelet channel are actually due to lamellar body particles present in the amniotic fluid. Most platelet channels measure all particles between 2 and 20 fL in volume. Most of the lamellar bodies fall within this size range. Vaginal pool specimens give artificially high counts and therefore should not be used. This prediction is important in many obstetric situations, including premature labor, premature rupture of the membranes, management of eclampsia, fetal distress, and elective delivery at term.
Pulmonary surfactant is composed almost entirely of surface active phospholipids.
Lamellar bodies first appear in the cytoplasm of fetal pneumocytes between 20-24 weeks gestation. Fetal breathing movements and a net exudation of fluid carry lamellar bodies into the amniotic fluid, where they can then be counted. The phospholipid content and the laminated structure of these particles change with maturation of the fetal lung. By assessing the number and size distribution of lamellar bodies within the amniotic fluid, fetal lung maturity can be predicted. Clinical chemistry of pregnancy.