Prediction of respiratory distress syndrome

Abstract

To the Editors: We were pleased to read Stubblefield's editorial1.Stubblefied P.G. Using the TDx-FLM assay and gestational age together for more accurate prediction of risk for neonatal respiratory distress syndrome.Am J Obstet Gynecol. 2002; 187: 1429-1430Abstract Full Text Full Text PDF PubMed Scopus (9) Google Scholar emphasizing the need to combine gestational age and fetal maturity testing results in predicting the probability of respiratory distress syndrome (RDS). We agree that this is an important concept that has not been commonly accepted. However, in both his editorial and the case report by Pinette et al2.Pinette M.G. Blackstone J. Wax J.R. Cartin A. Fetal lung maturity indices—a plea for gestational age–specific interpretation: a case report and discussion.Am J Obstet Gynecol. 2002; 187: 1721-1722Abstract Full Text Full Text PDF PubMed Scopus (20) Google Scholar we believe that clarification is needed. In both the case report and the editorial, the stated reference point for maturity is incorrect. The FLM-II, the only version of the assay available since 1995, uses as its reference point for maturity a value above 55 mg surfactant/g albumin. It was the original version that used a value above 70 mg/g. In addition, the table included in the case report is in error because it is derived from an analysis also using the original, rather than the current, reference point. That report by Tanasijevic et al3.Tanasijevic M.J. Wybenga D.R. Richardson D. Greene M.F. Lopez R. Winkelman J.W. A predictive model for fetal lung maturity employing gestational age and test results.Am J Clin Pathol. 1994; 102: 788-793PubMed Google Scholar was published in 1994, before the transition to the new FLM-II assay. It should also be noted that, in the patient population used in that analysis, the prevalence of RDS was 5.7%. This rate may not accurately reflect other populations, where the prevalence may be as high as 15%. A recently published article by Kaplan et al4.Kaplan L.A. Chapman J.F. Bock J.L. Santa Maria E. Clejan S. Huddleston D.J. et al.Prediction of respiratory distress syndrome using the Abbott FLM-II amniotic fluid assay.Clin Chim Acta. 2002; 326: 61-68Crossref PubMed Scopus (21) Google Scholar also addresses the combination of gestational age and fetal maturity testing results (the FLM-II) in predicting the likelihood of RDS. Probabilities and odds ratios based on assay results are provided for gestational age ranges (<34, 34-36, >36 weeks) rather than for specific weeks of gestation. Prevalence of RDS is also taken into account. Given the imprecision of gestational age determination, the influence of other factors on the neonatal course, and the difficulty in diagnosing RDS (especially when mild), such grouping of gestational week data seems more appropriate than calculating such risks by individual weeks of gestation. Finally, the value of performing multiple tests of fetal maturity, as described in the case report, has been questioned. Clinically, results may vary (as occurred in this case) and certainly the cost is higher with protocols involving multiple tests as a routine. The value of a “cascade” or “sequential” testing approach—subsequent testing based on results of an initial test—has been advocated.5.American College of Obstetricians and Gynecologists Assessment of fetal lung maturity. The College, Washington (DC)1996Google Scholar