Fetal Lung Maturity Testing Research Articles

Assay of disaturated phosphatidylcholine in amniotic fluid as a test of fetal lung maturity: experience with 2000 analyses.

We determined concentrations of disaturated phosphatidylcholine (DSPC) in nearly 2000 amniotic fluid samples obtained either transabdominally or as vaginal pools. Here we report our comparison of these DSPC values with the lecithin/sphingomyelin (L/S) ratios for amniotic fluid samples obtained from diabetic and nondiabetic pregnancies and also between transabdominally or vaginally collected samples uncontaminated by blood or meconium. DSPC measurement is at least as good as the L/S ratio in predicting the absence of respiratory distress syndrome. DSPC concentrations were, however, lower in diabetic than in nondiabetic pregnancies, supporting the hypothesis that DSPC synthesis may be impaired in fetuses of diabetic mothers. Visually uncontaminated samples collected transabdominally or vaginally, when grouped according to length of gestation, have similar DSPC values but different L/S ratios. Thus, even in the absence of blood or meconium, DSPC may be a more useful test than the L/S ratio for vaginally pooled samples.

Cholesteryl palmitate as a predictor of fetal lung maturity

Cholesteryl palmitate was measured by thin-layer chromatography in 98 amniotic fluid samples obtained from pregnancies ranging from 15 to 40 weeks. Pregnancies complicated by diabetes mellitus or Rh sensitization were excluded. Cholesteryl palmitate concentration increased with gestational age from values less than 5 micrograms/ml at 15 weeks to maximum values of 384 micrograms/ml at term. Seventy-three patients were delivered of their infants within 24 hours of sampling. The mean concentration of cholesteryl palmitate for 55 infants without respiratory distress syndrome was 123.70 +/- 12.21 micrograms/ml (SD). For neonates that developed respiratory distress syndrome (n = 18), the mean concentration was 22.66 +/- 6.16 micrograms/ml (SD). This difference is significant (p less than 0.001). For all patients delivered, respiratory distress syndrome was not seen when the cholesteryl palmitate concentration was greater than 41 micrograms/ml (mean + 3 SD). All infants with a concentration below 38 micrograms/ml developed respiratory distress syndrome. We conclude that measurement of cholesteryl palmitate concentration in amniotic fluid might be another reliable method of assessing fetal lung maturity and may often improve specificity when compared with other tests of fetal lung maturity.

Clinical and economic considerations associated with testing for fetal lung maturity

Performing multiple tests of fetal lung maturity on amniotic fluid samples may not use the individual test results and laboratory personnel most effectively. To determine the best strategy for fetal lung maturity testing, we analyzed our experience with use of a variety of procedures. Clinical usefulness was assessed according to sensitivity, specificity, predictive values, and efficiency. Economic and technical aspects analyzed included time and personnel requirements, availability of tests, and expense of each procedure. Several testing sequence approaches were compared for efficiency and cost. In our laboratory the foam stability index proved to be the most useful initial test of fetal lung maturity, reserving more expensive and time-consuming tests for instances in which the foam stability index is immature. Routine multiple testing did not enhance clinical usefulness and greatly increased costs. Development of a testing strategy using a rapid, inexpensive, and widely available test such as the foam stability index would promote clinical and economic efficiency.

Disaturated phosphatidylcholine as a fetal lung maturity test: Lack of interference by seminal ejaculate as a contaminant in vaginally pooled amniotic fluid samples

Seminal ejaculates obtained from four men were added to amniotic fluid pools. Lecithin/sphingomyelin ratios in amniotic fluid were significantly lowered in the presence of small amounts of contaminating semen. In contrast, the determination of disaturated phosphatidylcholine was not affected by the presence of this contaminant.

Prediction of fetal lung maturity by use of the Lumadex-FSI test.

We analyzed amniotic fluid from 91 pregnancies (estimated gestational age range 31 to 41 weeks), using the Lumadex-FSI Fetal Lung Maturity test (Beckman Instruments), and also determining phosphatidylglycerol content, the lecithin/sphingomyelin ratio, and foam stability index by the "shake test," and compared results with newborn outcome. Five of 64 babies born within 72 h of testing developed hyaline membrane disease. Except for the lecithin/sphingomyelin ratio, the predictive value of a negative test was 100% but that of a positive test was less than 50%. Use of all four tests did not offer diagnostic advantage over the use of Lumadex-FSI alone. For the laboratory that infrequently assesses fetal lung maturity, we believe the sealed cassette format of the Lumadex-FSI will permit better quality assurance than the shake test. The Lumadex-FSI test is intended to provide a graded estimate of positive risk for hyaline membrane disease, but more data from different centers and patient populations are needed to establish reliable predictive values.

Fluorescence polarization values of amniotic fluid collected from the vagina after rupture of the membranes

Transvaginal collection of amniotic fluid and the use of a reliable test for fetal lung maturity will provide information needed in the management of patients with premature rupture of the membranes.

Diagnostic tests in obstetrics: A method for improved evaluation

With the proliferation of diagnostic tests in obstetrics, several recurrent questions arise. How does one determine whether one diagnostic test is superior to another available test? What test cutoff value best separates diseased from nondiseased patients? How much does performance of additional tests assist in arriving at a correct diagnosis? This article reviews a simple yet sophisticated analytic technique, the receiver operating characteristic curve, and demonstrates its application to several obstetric diagnostic tests. Receiver operating characteristic curve analysis is used to select a cutoff value for the 1-hour glucose tolerance test, to compare amniotic fluid tests of fetal lung maturity, and to determine the optimal combinations of factors and overall performance of the fetal biophysical profile. The value of receiver operating characteristic curve analysis lies in providing a clear graphic analysis of the performance of diagnostic tests over their entire range of values. It also provides the starting point for evaluating the costs and benefits of alternative cutoff points in differing clinical settings.

Absorbance of amniotic fluid at 650 nm as a fetal lung maturity test: A comparison with the lecithin/sphingomyelin ratio and tests for disaturated phosphatidylcholine and phosphatidylglycerol

We compared absorbance of amniotic fluid at 650 nm (A650) against the lecithin/sphingomyelin ratio, the quantity of disaturated phosphatidylcholine, and the presence or absence of phosphatidylglycerol in 374 uncontaminated amniotic fluid samples. In addition, we studied these measures of fetal lung maturity in 80 pregnancies where neonatal outcomes were known. Statistical analysis revealed a significant association between increasing absorbance and biochemical indices of lung maturation. Our results indicate that A650 of amniotic fluid is useful as a measure of lung maturity but that the greatest utility may be for samples with either low absorbance (<0.10) or high absorbance (>0.20). Because of large false positive and false negative values between these two absorbances, other lung maturity estimates should be used when absorbances fall within this range. Therefore, A650 may be most useful as a screen or as part of a battery of lung maturity estimates. We are exploring these possibilities as a means of providing better fetal lung maturity estimates.

Amniotic fluid phospholipids after maternal administration of dexamethasone

The administration of corticosteroids to pregnant women in premature labor can accelerate fetal lung development and potentially prevent neonatal respiratory distress syndrome (RDS). Controversy exists, however, as to whether amniotic fluid phospholipid indices of lung maturation are influenced by such treatment. Without a suitable test for evaluating the fetal response to corticosteroids, there is no method of recognizing whether and when lung development has been stimulated. In an attempt to resolve this issue, we carried out a study of amniotic fluid phospholipids as part of the National Institutes of Health multicenter trial of prenatal corticosteroids. Amniocenteses were performed before the administration of either steroid hormone or placebo and approximately 1 week after a series of four injections was initiated. Analysis of the ratio of lecithin (phosphatidylcholine) to sphingomyelin (L/S ratio) revealed nearly identical values initially and no significant difference in the posttreatment means when 25 steroid-treated pregnancies were compared to 20 control pregnancies. Although there were significant increases in both groups during the interval between amniocenteses, no statistical difference was found in the extent of change in L/S ratios between the two groups, when pretreatment values were compared with those obtained an average of 1 week later. In addition to evaluating L/S ratios, we performed an assessment of phospholipid concentrations in 17 pregnancies before and after administration of dexamethasone. This revealed no detectable phosphatidylglycerol. There were increases in the absolute concentrations of phosphatidylcholine and disaturated phosphatidylcholine, but these changes were relatively modest in magnitude and could be attributable to either advanced gestational age or dexamethasone. Our results demonstrate that current tests of fetal lung maturity do not provide a routine means for prenatal detection of pulmonary maturational responses to corticosteroids.

A modified activated partial thromboplastin time with the use of amniotic fluid: Preliminary report of a new technique for detection of fetal lung maturity

The need for a simple, accurate, rapidly performed fetal lung maturity test remains unfilled despite the large number of methods available. In a preliminary prospective study, the amniotic fluid activated partial thromboplastin time (PTT) appeared to be encouraging. The false mature rate in an at-risk patient population was 0.80%, and the false immature rate was 61%. The false mature rates for the lecithin/sphingomyelin ratio and absorbance 650 in the same patients were 0% and 0.63%, respectively, whereas the false immature rates were 81.8% and 91.3%. Since both the amniotic fluid activated PTT and absorbance 650 can be readily performed in the smallest hospital, the accuracy of the combination was explored. Combining the amniotic fluid activated PTT with a mature absorbance 650 reduced the false immature rate to 30.7%. The amniotic fluid activated PTT is a rapid, accurate, economical test that is unaffected by gross blood or meconium contaminants.

Improved prediction of fetal lung maturity in diabetic pregnancies: A comparison of chromatographic methods

Following planned termination of pregnancy, infants of diabetic mothers have shown a continued vulnerability to the respiratory distress syndrome (RDS), suggesting false positive results on fetal lung maturity testing. We studied the adequacy of the standard one-dimensional chromatographic lecithin/sphingomyelin (L/S) ratio for predicting RDS in 56 diabetic and 50 nondiabetic pregnancies. An exceptionally low incidence of RDS was noted for the study (0.95%) as well as for diabetic pregnancies alone (1.85%). The clinical results were further compared to a new method for determining L/S ratios and identifying other pulmonary phospholipids by two-dimensional chromatography. Values for two-dimensional L/S ratios were significantly lower from 36 through 38 weeks' gestation (P less than 0.01), suggesting improved accuracy and a lessened risk for false positive results in preterm deliveries. Positive identification of amniotic fluid phosphatidylglycerol (PG) was related to increasing L/S ratios (P = 0.001), but only 50% of nondiabetic and 16.7% of diabetic amniotic fluid samples contained PG when the L/S was 2:1 or greater (P = 0.02). The identification of PG serves to confirm fetal lung maturity, but the L/S ratio remains the best available indicator of fetal lung maturity for all high-risk pregnancies.

1286 IMPROVED PREDICTION OF FETAL LUNG MATURITY IN DIABETIC PREGNANCIES

Following planned termination of pregnancy, infants of diabetic mothers (IDM) have shown a continued vulnerability to the respiratory-distress syndrome (RDS) suggesting false-positive fetal lung maturity testing. Adequacy of the lecithin/sphingomyelin (L/S) ratio for predicting RDS was studied in 56 diabetic (DM) and 50 nondiabetic (ND) pregnancies. Amniotic-fluid samples (n=130) were assayed for 1- and 2-dimensional (dim) thinlayer chromatographic (TLC) L/S ratios, and phosphatidylglycerol (PG) and phosphatidylinositol (PI) assays. L/S ratios for all pregnancies by both TLC techniques revealed higher 1-dim values from 36-38 wk gestation (P 38 wk with L/S ratios > 3. PG detection by class of DM was delayed for class A pregnancies beyond 36.5 wk (r=0.6551, P<0.007). Respiratory distress developed in 3 infants (2.9%): 2 ND had transient tachypnea (1.9%), 1 IDM had RDS (0.95%). We conclude: 1) 2-dim TLC improves phosphatide identification, 2) PG, if present, confirms fetal lung maturity in conjunction with positive L/S ratios, and 3) the L/S ratio remains the best available indicator of fetal lung maturation, irrespective of maternal diabetes.

Improved thin-layer chromatography of disaturated phosphatidylcholine in amniotic fluid.

We describe an indirect test of fetal lung maturity: the quantitation of disaturated phosphatidylcholine in amniotic fluid. The lipids in samples of amniotic fluid from 172 patients were reacted with osmium tetroxide, and disaturated phosphatidylcholine was then isolated by thin-layer chromatography. Interfering substances were retained by a pre-adsorbent layer. The charred disaturated phosphatidylcholine, quantitated by densitometry, was compared to standard dipalmitoyl phosphatidylcholine. Both within-run and between-run coefficients of variation were about 10%. Blood and meconium do not interfere. Six infants developed respiratory distress when disaturated phosphatidylcholine concentrations of amniotic fluid drawn within 72 h of delivery were less than 5.5 mg/L. A concurrently determined lecithin/sphingomyelin ratio falsely predicted lung maturity in one of these. In seven other samples for which lecithin/sphingomyelin ratios suggested lung immaturity but disaturated phosphatidyl-choline predicted maturity, none of the infants developed respiratory distress. In normal pregnancies, measurement of disaturated phosphatidylcholine in amniotic fluid appears to be a better predictor of fetal lung maturity than is measurement of the lecithin/sphingomyelin ratio. Further studies are needed to determine if this analysis is a better predictor in diabetic pregnancies.

Effect of gestational variation of phosphatidylglycerol and phosphatidylinositol on the microviscosity of amniotic fluid phospholipids.

Amniotic fluid microviscosity, as measured by 1,6-diphenylhexatriene fluorescence polarization, shows an excellent correlation with the most frequently performed test for fetal lung maturity, the Iecithin-sphingomyelin ratio, and is an excellent predictor of respiratory distress syndrome. On the basis of reported percentages of amniotic fluid phospholipids and their variation during gestation, we prepared and measured the microviscosity of phospholipid dispersions with compositions corresponding to amniotic fluid at gestational ages of 35 weeks. Microviscosity of these dispersions decreases with increasing gestational age. Furthermore, physiologic variations in phosphatidyiglycerol and phosphatidylinositol, especially the former, within each gestational period can greatly influence microviscosity values: as either phospholipid was increased in each gestational period, the microviscosity values decreased in a stepwise pattern. Microviscosity measurements are, therefore, sensitive to physiologic variations in all phospholipids important for fetal lung maturity determinations, not just lecithin and sphingomyelin. From this and previous studies we conclude that amniotic fluid fluorescence polarization measurements have diagnostic and technical advantages over the lecithin-sphingomyelin ratio as a test for fetal lung maturity.

1002 MECONIUM STAINED (MS) AMNIOTIC FLUID - A USEFUL ANTENATAL INDEX OF FETAL MATURITY AND RISK TO HMD

A negative implication is commonly associated with MS amniotic fluid. Most frequently, it is indicative of fetal distress or asphyxia. We report that the finding of MS amniotic fluid has a positive, clinical usefulness. It is a highly accurate antenatal index of fetal maturity and the risk of the infant to HMD.From 1973-1976, we reviewed the maturity and incidence of HMD among 1165 MS infants. Gestational age in LBW infants was assessed by the Dubowitz score. Of the total 1165 infants, 909 (78%) were mature; 170 (15%) were postmature and 77 (7%) were premature. Among the premature infants, 82% were ≥35 wks; 10% were 34 wks; 7% were 32-33 wks and 1% was <32 wks. Since asphyxia is a potent stimulus to the fetal passage of meconium, we determined the incidence of MS amniotic fluid in a group of infants with 1 minute Apgar ≥6 (N=555). Of the 555 infants, 36.3% of the full-term and 68.2% of the postmature passed meconium, as compared to only 2.6% of the prematures (p<0.01). The exception was noted in infants of drug dependent mothers (IDDM). Out of 56 premature IDDM with low Apgar, 20% had MS amniotic fluid.The incidence of HMD among MS infants was very low (0.5%). Thus, the finding of MS fluid surpasses the predictability of many antenatal tests of fetal lung maturity including the L/S ratio. The incidence of HMD among premature MS infants was 8% as compared to 17% in our general premature population (p<0.05). This difference is related to the large percentage (82%) of premature MS infants being ≥35 wks gestation.CONCLUSION: MS amniotic fluid correlates highly to fetal maturity. Only in 7% will the infants be premature and most (82%) will be ≥35 wks. The only exception is with the IDDM, because of the association of MS with fetal drug withdrawal. The incidence of HMD among MS infants is 0.5%. Thus MS amniotic fluid can be an accurate indicator of fetal lung maturity.

The use of the amniotic fluid lecithin/sphingomyelin (L/S) ratio, creatinine concentration and nile blue sulphate tests, individually and in combination, in the assessment of fetal lung maturity.

The lecithin-sphingomyelin (LS) ratio is a good, but not absolute, test of fetal lung maturity. A total of 373 infants was delivered within 72 hours of amniotic fluid collection for assessment of the L/S ratio. Five of 43 infants (11-6 per cent) with an L/S ratio of 2-2 or less developed the respiratory distress syndrome (RDS), whereas only one of 320 infants (0-31 per cent) with a higher L/S ratio developed RDS. The risk of RDS could be further defined by using the creatinine concentration (critical value 19 mg/1) and the Nile blue sulphate test (critical value 4 per cent) in combination with the L/S ratio. All three tests were performed in 320 pregnancies and in each instance delivery took place within 72 hours. When all three test results were low, 3 of 5 infants (60 per cent) developed RDS, whereas when all three results were high, none of 175 infants developed RDS. When one or two results were low, 2 of 140 infants (1-4 per cent) developed RDS.

Determination of amniotic fluid total phospholipid phosphorus as a test for fetal lung maturity

Determinations of amniotic fluid lecithin phosphorus (Lec. P) and total phospholipid phosphorus (TPP) have been made at varying stages of gestation. The level of Lec. P demonstrates about a tenfold increase and TPP about an eightfold increase from 30 weeks' gestation to term. Simultaneous measurements of Lec. P and TPP have been made in a series of samples collected at delivery. A high correlation coefficient is found between the two measurements. In 12 samples associated with infants who developed the respiratory distress syndrome (RDS), the levels of both Lec. P and TPP were seen to be clustered at the low end of the spread of values. It would appear that a determination of TPP can be used for evaluation of fetal pulmonary maturity where it is impractical for one reason or another to perform the more precise determination of Lec. P. At the present time, if TPP is used for this purpose, it is recommended that a value of 0.140 mg. per 100 ml. or greater be used as indicative of pulmonary maturity. This minimal value provides a good margin for error since the majority of infants with RDS were associated with levels less than 0.041 mg. per 100 ml.

Rapid specific determination of amniotic fluid lecithins as a test of fetal lung maturity.

Normal respiratory function in the newborn depends on the development of adequate amounts of surf actant substances in the alveoli. The changes in the phospholipid content of the fetal lung during gestation correspond to those in the amniotic fluid. Therefore several methods have been developed to determine the amount of amniotic fluid lecithins, which are major constituents of surfactant substances and which, in contrast to the other main phospholipids, are greatly increased in the last trimester of gestation, especially near term. GLUCK et al. [3] have described a method for estimating the liquor lecithin/sphingomyelin ratio (L/S ratio). Some authors corroborated their results [1,5,7,11]; others came to different conclusions [4, 8,12]. GUSDON and WAITE [4] proposed a colorimetric method for the determination of phospholipids in amniotic fluid, 70 % of which are thought to consist of lecithins. There is no doubt that analysis, based on such measurements, is both unsatisfying and unreliable. In addition, determination of phosphorus is unspecific. Therefore, complete Separation of lecithins before determination is necessary. Some authors have achieved this objective by separating lecithins from other phospholipids using thin-layer chromatography and measurement of phosphorus in the eluate from silica gel scraped from the plate. The disadvantages of this method are the long-time periods involved, recovery problems (recovery: 86—92% [1]) and high liquor volumes (8 to 18 ml [l, 8, 9]). These facts give an idea of what is needed: A method for direct determination of lecithins Curriculum vitae