Optimal thresholds of the lecithin/sphingomyelin ratio and lamellar body count for the prediction of the presence of phosphatidyl glycerol in diabetic women

Objective: To assess the optimal thresholds of the lecithin/sphingomyelin (L/S) ratio and lamellar body count for the prediction of the presence of phosphatidyl glycerol (PG) in diabetic pregnant women. Methods: We accessed a database of clear amniotic fluid specimens obtained by transabdominal amniocentesis in diabetic women with singleton non-malformed fetuses. PG results were classified as 'absent' or 'present'. Receiver operating characteristic (ROG) curve analysis was constructed of different L/S ratios and lamellar body counts to identify the optimal threshold for prediction of the presence of PG. Sensitivity was defined as the rate of L/S ratio and lamellar body count above specific thresholds among cases with present PG. The false-positive rate was that of L/S ratios or lamellar body counts above specific thresholds among cases with absent PG. Statistical analysis included one-way analysis of variance with post-hoc analysis, with p < 0.05 considered significant. Results: A total of 76 consecutive women were inclucled in the analysis, 74% (n = 56) using insulin and the remainder treated by diet alone. L/S and PG results were both available in 72 women. PG was reported as 'present' in 70% (51/73) of specimens. As expected, there was a significant relationship between L/S ratios and presence of PG (area under the curve = 0.932, p < 0.001). An L/S ratio of ≥ 3.0 represented the optimal trade-off between sensitivity (68%) and false-positive rate (6%) in the prediction of present PG. Similarly, there was a significant relationship between lamellar body count values and presence of PG (area under the curve = 0.976, p < 0.001). A lamellar body count of ≥ 50 000 represented the optimal trade-off between sensitivity (92%) and false-positive rate (0%) in the prediction of present PG. Conclusion: In diabetic pregnant patients, the presence of PG in the amniotic fluid more closely corresponded to an L/S ratio of ≥ 3.0 or to a lamellar body count of ≥ 50 000.