Amniotic fluid lamellar body count: Cost-effective screening for fetal lung maturity

Objective: To create a highly specific cascade testing scheme for fetal lun g maturity using the lamellar body count, lecithin/sphingomyelin ratio (L/S ), and phosphatidylglycerol. Methods: A nondedicated hematology analyzer (Sysmex NE 1500, Toa Medical El ectronics, Los Angeles, CA) was used to determine the lamellar body counts of 209 unspun amniotic fluid specimens. Maximally specific lamellar body co unt cutoffs for biochemical maturity and immaturity were determined using r eceiver operating characteristic curves. Biochemical lung maturity was defi ned as either a mature WS ratio or phosphatidylglycerol. Biochemical lung i mmaturity was defined as both an immature L/S ratio and an immature phospha tidylglycerol. Results: A lamellar body count of less than 8000 (n = 17) was 100% specific for biochemical lung immaturity (positive predictive value = 100%, negativ e predictive value = 86%). A lamellar body count of greater than 32,000 was 98% specific for biochemical lung maturity (positive predictive value = 99 %, negative predictive value = 63%). Conclusion: Testing only specimens where the lamellar body count was greate r than 8000 and less than or equal to 32,000 for the LIS ratio and phosphat idylglycerol would preclude the need for 76% of all L/S and phosphatidylgly cerol assays. Because the lamellar body count is quick, simple, and univers ally available, it could serve as an extremely cost-effective screening tes t for fetal lung maturity. (C) 1999 by The American College of Obstetrician s and Gynecologists.