Evaluation of lamellar body number density as the initial assessment in a fetal lung maturity test cascade

The objective of this study was to assess the sensitivity and specificity of lamellar body number density in the prenatal prediction of the respiratory distress syndrome. Seventy consecutive amniotic fluid specimens obtained by amniocentesis within 72 hours of delivery were assessed for lamellar body number density, optical absorbance at 650 nm, lecithin/sphingomyelin ratio and phosphatidylglycerol. A maturity criterion of > or = 46,000/microL for lamellar body number density yielded values for diagnostic sensitivity of 100% (7/7), specificity of 89% (49/55), positive predictive value of 54% (7/13) and negative predictive value of 100% (49/49). These values were also determined for the other analytes, with results similar to those reported elsewhere. Lamellar body number density is an effective and inexpensive first test for the rapid identification of the fetus at high risk for the respiratory distress syndrome. A cascade approach, using lamellar body number density as the first test and optical absorbance at 650 nm as the second test, improves the predictive value as compared to any single test of fetal lung maturity.