Racial differences in the predictive value of the TDx fetal lung maturity assay

Black newborns have lower rates of neonatal respiratory distress syndrome compared with nonblack newborns. This has been attributed to accelerated lung maturation. Previous studies have demonstrated a difference in the predictive value of the lecithin/sphingomyelin ratio, a test for lung maturity, between races. Our study examines the predictive value of the newer TDx Fetal Lung Maturity Surfactant-to-Albumin assay.

We reviewed the records of 393 nonblack and 87 black infants delivered within 72 hours of the TDx FLM S/A assay testing. We compared the rates of neonatal respiratory distress syndrome by race, stratified by results.

In our study population black newborns had less than one half the rate of respiratory distress syndrome compared with nonblack newborns (4.6% vs 10.4%). To adjust for possible differences in the timing of lung maturation, the results were stratified by the TDx FLM S/A assay result. Black race had a protective effect (Mantel-Haenszel weighted odds ratio 0.30, 95% confidence interval 0.06 to 0.93, p < 0.05). This significant racial difference remained when both TDx FLM S/A assay result and gestational age were controlled in a multiple logistic regression analysis.

There are differences in the predictive value of the TDx FLM S/A assay among races. Black fetuses are less likely to have respiratory distress syndrome. The difference in rates of respiratory distress syndrome between races must be due to either a qualitative difference in the surfactant or to an anatomic difference in fetal lungs. Consideration should be given to a lower cutoff value for a mature test result in black women.