Pulmonary lamellar bodies in human amniotic fluid: their relationship to fetal age and the lecithin/sphingomyelin ratio.

We investigated the appearance of pulmonary lamellar bodies (LBs) in human amniotic fluid as a function of fetal age. We also studied their relationship to the lecithin/sphingomyelin (L/S) ratio and to the results of the rapid surfactant test (RST). LBs observed in amniotic fluid generally ranged in diameter from 1.5 to 2.0 mu and were seen as single structures or in clusters. When patients were grouped by gestational age, there was a significant difference (P less than 0.001) in the distribution of amniotic fluid LBs. No LBs were observed in amniotic fluid before 26 weeks' gestation, but 50% of specimens at 28 to 32 weeks' gestation and 85% of specimens at term had LBs. Patients with amniotic fluid LBs had higher L/S ratios and intermediate or mature RST values when compared to patients without LBs, but a statistically significant relationship between the presence of LBs and the L/S ratio or RST was not found. We conclude that qualitative examination of amniotic fluid LB content by conventional electron microscopy is unlikely to reflect fetal lung maturation in a precise manner. However, direct quantification of LBs may provide a more specific index of fetal lung maturity and the risk of respiratory distress syndrome.