Strategic utilization of fetal lung maturity tests

Fetal lung maturity

Respiratory distress syndrome of the newborn infant caused by immaturity of the fetal lung continues to be a clinical problem. Measurement of pulmonary surfactant production is the most effective way to evaluate pulmonary maturity. Since the first fetal lung maturity test was described more than two decades ago, advances in methodology have produced diagnostically sensitive tests that are both rapid and precise. Unfortunately, currently available tests continue to demonstrate low diagnostic specificity and remain poor predictors of fetal lung immaturity. We review the background, methodology, pre-analytical and analytical concerns, and clinical performance of various fetal lung maturity assays, and discuss the appropriate use and interpretation of these tests.

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 < or = 22,000/microL was obtained. Diagnostic accuracy (and confidence interval, CI) 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 (< or = 22,000 vs. < or = 20,000/microL), 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.

Evaluation of the effect of meconium on assessment of fetal lung maturity status by TDxFLM II testing

OBJECTIVE

To evaluate the effect of meconium contamination on the TDxFLM II assay.

METHODS

Amniotic fluid was collected from patients undergoing amniocentesis for obstetric indications between 31 and 40 weeks of gestation. A baseline TDxFLM II value was obtained and compared with amniotic fluid contaminated with 1%, 5%, and 10% meconium by weight.

RESULTS

Twenty-one samples were studied, and in every case the TDxFLM II value decreased once the meconium was added. There was no consistent rate of decrease that correlated with the percentage of meconium added.

CONCLUSION

Meconium contamination decreases the TDxFLM II value. A clinician who performs this test in the presence of meconium can be reassured that the contamination will not give an artificially elevated result. If the result is in the mature range, one can be confident that the result would only be higher if meconium were not present.

Testing for fetal lung maturation: a biochemical "window" to the developing fetus

Fetal lung maturity testing represents a major milestone in perinatology. This article critically evaluates specific controversies regarding the methodologies used to measure pulmonary surfactant in AF and how well each of these techniques performs both in principle and application. The clinical utility of fetal lung maturity testing as it applies to particularly difficult complications of pregnancy is discussed. These technical and clinical issues are framed by the scientific and empiric evidence that is used as the rationale for such testing and its implementation in the effective management of preterm delivery.