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What is the optimal lamellar body count for predicting fetal lung maturity?

      Objective

      The lamellar body count in amniotic fluid appears to be a reliable indicator of fetal lung maturity. Different methodologies and cut-off values for maturity have been suggested. Recently, a concensus panel suggested a cut-off of 50,000 for non-centrifuged specimens. We sought to assess the validity of this cut-off in our population and determine the impact of a lower cut-off at our center.

      Study design

      We assessed Lamellar body counts, TDX FLM, Lecithin sphingomeylin ratios(L/S), and phosphatidylglycerol levels in women undergoing amniocentesis after 30 weeks. All specimens were filtered but not centrifuged. Receiver operator curves were used to evaluate the area under the curve of lamellar body counts compared to the other tests as well as the occurrence of RDS. Sensitivity, specificity, negative predictive values and positive predictive values were calculated for fetal lung maturity using different cutoffs for lamellar body counts.

      Results

      A total of 245 women met the inclusion criteria. Ninety nine women delivered within 72 hours of amniocentesis with 23 percent of their fetuses developing RDS. The performance of the test characteristics are presented in the two tables below. In our series, if the cutoff were lowered to 45,000, we would have encountered only one additional case of RDS among 9 delivered fetuses.

      Conclusion

      Our data suggest that lowering the cut-off of lamellar body count to 45,000 would not significantly compromise the negative-predictive value of the test.
      Tabled 1Comparision of tests of fetal lung maturity(AUC)
      THX FLMLS>2PG Pos
      Lamellar body0.890.820.71