Fetal lung maturity assessment by a modified A650determination

Publisher Website
Google Scholar
Abstract
This paper presents an evaluation of a modified absorbance method for estimating fetal lung maturity. Absorbance at 650 nm in combination with a two-step centrifugation procedure was used in an attempt to focus more directly on lamellar bodies and evaluate the contribution of residual absorbance due to non-lamellar body materials. Absorbance values after centrifugation at 250 .times. g for 5 minutes (A250) and 10,000 .times. g for 20 minutes (A10,000) were taken as estimates of total absorbance due to lamellar bodies plus non-lamellar body material and that due to non-sedimentable, non-lamellar body material, respectively. .DELTA.A (A250-A10,000), to better estimate absorbance due to lamellar bodies, and %A (.DELTA.A/A250 .times. 100), to express lamellar body absorbance in terms of total observable absorbance and thereby minimize effects of dilution. The three parameters (A250, .DELTA.A, %A) were used in combination to create a battery (ABatt) of absorbance values for each fluid sample. Absorbance after centrifugation at 2,000 .times. g for 10 minutes (A2,000), a widely used standard method, was also evaluated for purposes of comparison. A250 was designated as mature if greater than or equal to 0.350, .DELTA.A was called mature if greater than or equal to 75%. If any of the parameters was immature, ABatt was called immature. The range of values for A250, A2,000, and A10,000, (figure 1) increased with gestational age in the total population as well as the corrected population (excluding amniotic fluid contaminants, and pregnancies with isoimmunization or diabetes). Median values for A250 increased more than A2,000 with advancing gestational age. Non-sedimentable, residual absorbance (A10,000) also increased with advancing gestational age, however, its relative contribution to A250 is less than to A2,000 beyond 36 weeks gestation. The second portion of the study was to evaluate the relationship between L/S values, absorbance parameters and newborn complications when delivery occurred within three days of amniotic fluid sampling. The non-occurrence of HMD was most accurately predicted by the L/S ratio in the total population (Tab. II), and equally by all three methods in the corrected population. False predictions of maturity on the basis of absorbance data were eliminated when the sample population was restricted to uncontaminated specimens obtained in the absence of maternal diabetes, isoimmunization and premature rupture of membranes. This study demonstrates that the non-occurrence of HMD can be predicted by either the L/S ratio, the ABatt or the A2,000 method. The data suggest that the usefulness of ABatt derives principally from amniotic fluid lamellar bodies, while both lamellar bodies and non-sedimentable material contribute to A2,000.