The effect of polyhydramnios on fetal pulmonary maturity studies: An in-vitro model

OBJECTIVE: To test the hypothesis that polyhydramnios increases the false negative rate of" fetal lung maturity studies. STUDY DESIGN: Fluid obtained at amniocentesis from term gestations during a 3 month period was stored at -70° C. The samples from patients who had a mature Fetal Lung Maturity test (FI.M, Abbot TDx-FI.x > 50 g/mg albumin) were then thawed and divided into aliquots of 1:1, 1:4 and 1:8 dilutions using the supernatant from early second trimester genetic amniocentesis samples which had been centrifuged at 1,000 rpm for 10 min and then frozen until use. Lecithin/Sphingomyelin (I./S, Helena Fetal-Tek 200), FLM and Phosphatidyl glycerol (PG, ÄmnioStat-FI.M) were determined at (he different dilutions. PG was considered present if the concentration was > 0.1? |j.g/ml. RESULTS: Specimens from 15 patients were included. Freezing did not significantly change the FI.M results. Dilution significantly decreased the FI.M and L/S values and the number of'PG positive samples. Of the 3 tests, the PG had the lowest false negative rate following dilution. CONCLUSIONS: Our findings support the hypothesis that diluting the amniotic fluid, such as may occur with polyhydramnios, may result in false negative fetal lung maturity studies. Of the three most commonly used tests, the P(i assay has the lowest false negative rate.