Amniotic fluid lamellar body counts for the determination of fetal lung maturity: an update

Aim: To reassess the cut-off value for lamellar body counts (LBs) for fetal lung maturity (FLM) over a 10-year study period. Patients and methods: 178 pregnancies were selected under strict inclusion criteria and delivered within 48 h from amniocentesis. FLM was determined by amniotic fluid LBs in centrifuged samples (300 x g for 10 min) in a commercially available Coulter Counter. Cases beyond 37 weeks were excluded. Results: Mean gestational age was 33.5 +/- 3.0 weeks at amniocentesis and 33.7 +/- 3.0 weeks at birth. After reassessing the best compromise between sensitivity and specificity for all cases using the receiver operating characteristic (ROC) procedure, an FLM cut-off value of <= 22,000/mu L was obtained. Diagnostic accuracy (and confidence interval, Cl) was: sensitivity, 73% (60.0-83.6%); specificity, 81.7% (CI 73.6-88.1%); positive predictive value, 66.2%; and negative predictive value, 86.0%. Conclusion: No significant change in FLM cut-off for LBs was found when comparing the value from this study and the results of our earlier report presented in 1996 (<= 22,000 vs. <= 20,000/mu L), although the new value may be more accurate, since it is based on neonatal outcome with the exclusion of cases in which the diagnosis of FLM is seldom warranted, i.e., > 37 weeks' gestational age.