Neonatal Respiratory Distress Syndrome as a Function of Gestational Age and the Lecithin/Sphingomyelin Ratio

by St. Clair, Caryn M.

This study was designed to derive predictive logistic regression equations to allow the risk of neonatal respiratory distress syndrome (RDS) to be defined as a function of both the lecithin/sphingomyelin (L/S) ratio and gestational age. We hypothesize that the optimal cutoff value will vary significantly depending on gestational age, and that our data will support the need to account for gestational age when interpreting test results.

Data was collected via a retrospective chart review. Women who underwent amniocentesis for the purpose of assessing fetal lung maturity at Yale-New Haven Hospital from 1998 to 2004 were identified and included if delivery of a liveborn, singleton, non-anomalous infant occurred within 72 hours of the lecithin/sphingomyelin ratio assay. Maternal and neonatal data were collected regarding demographics, pregnancy complications and neonatal outcomes, including respiratory distress syndrome.

A total of 210 mother-neonate pairs met criteria for analysis, with 8 cases of RDS. Both gestational age and L/S ratio were independent predictors of RDS. By modeling the odds of RDS using logistic regression, a probability of RDS approximating 10% was noted at an L/S cutoff of 3.6 at 32 weeks, 2.8 at 34 weeks, 1.8 at 36 weeks, and 1.4 at term. Under 32 weeks of gestation a probability as low as 10% was not observed by this model. We conclude that stratifying risk of neonatal RDS using both the L/S ratio and gestational age may aid in clinical decision-making concerning the timing of delivery.