General Obstetrics and Gynecology Fetus-Placenta-Newborn
Comparison of infrared spectroscopic and fluorescence depolarization assays for fetal lung maturity,☆☆

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Abstract

Objective: Infrared spectroscopic analysis of amniotic fluid was recently shown to be a potential useful method for the determination of fetal lung maturity. Those studies used thin-layer chromatography as a reference method for the calibration of the infrared-based technique. However, thin-layer chromatography is compromised by large intra-assay and interlaboratory coefficients of variation. Therefore in this study we have used a reference method that is based on fluorescence depolarization, the TDx FLM II assay, to verify the sensitivity and precision of infrared spectroscopy for assessment of fetal lung maturity status. Study Design: Samples of amniotic fluid were obtained by amniocentesis from 101 patients between the 24th and 40th weeks of pregnancy. Small volumes (35 μL) of amniotic fluid specimens were dried, and the infrared spectra were measured with a commercial infrared spectrometer. The fetal lung surfactant/albumin ratio was determined separately for each specimen with the TDx FLM II assay. The proposed infrared method was then calibrated and tested with a partial least-squares regression analysis to quantitatively correlate the infrared spectra with the surfactant/albumin ratios provided by the TDx FLM II assays. Results: A total of 144 training spectra were used to build the partial least-squares calibration model. The correlation coefficient for the training set was excellent (r = 0.92), with an SE between infrared-predicted and reference surfactant/albumin ratios of 17 mg/g. The model was then validated on a set of 69 test spectra and yielded an SE of 14 mg/g (r = 0.86). The final partial least-squares model included the 900- to 1500-cm–1 and 2800- to 3200-cm–1 spectral ranges and 6 partial least-squares factors. Conclusion: Because the infrared-based fetal lung maturity measurements correlated well with assays from both of the current standard clinical techniques (thin-layer chromatography and fluorescence depolarization) and the procedure is less labor and training intensive, we concluded that infrared spectroscopy has the potential to emerge as the method of choice for prediction of fetal lung maturity from amniotic fluid analysis. (Am J Obstet Gynecol 2000;183:181-7.)

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Material

Amniotic fluid specimens from third-trimester pregnancies were acquired at the fetal assessment unit of the Health Sciences Center in Winnipeg. Indications for amniocentesis included planned elective cesarean delivery and complications of pregnancy necessitating early delivery. In total samples from 101 patients were examined. For each sample of amniotic fluid the surfactant/albumin ratio was determined by a trained medical technologist with the Abbott TDx Analyzer. These assays were calibrated

Results

The study group ranged from 25 to 40 weeks’ gestation, with the average being 35.3 ± 2.5 weeks’ gestation. Most requests for surfactant status are between 32 and 38 weeks’ gestation, which was representative of our normal samples. The relationship between surfactant/albumin ratio values and the gestational ages of the subjects in our study population is shown in Fig 1.

. Correlation between TDx FLM II surfactant/albumin ratio values and gestational age in study group.

Ideally, the

Comment

In the last 20 years many tests have been developed to assess fetal lung maturity by measuring different aspects of pulmonary surfactant.13, 14, 15 For instance, a 3-year prospective study demonstrated that lamellar body counting might be appropriate as a screening test for RDS in uncontaminated specimens.13 Another simple and rapid colorimetric assay has also been proposed for the simultaneous determination of lecithin, phosphatidylinositol, and phosphatidylglycerol in amniotic fluid.14 This

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Issued as National Research Council Canada publication No. 43154.

☆☆

Reprint requests: Henry H. Mantsch, PhD, Institute for Biodiagnostics, National Research Council Canada, 435 Ellice Ave, Winnipeg, Manitoba, Canada R3B 1Y6.

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