Amniotic fluid phosphatidylglycerol and the lecithin/sphingomyelin ratio in the assessment of fetal lung maturity

Rapid determination of fetal lung maturity from infrared spectra of amniotic fluid

OBJECTIVE

The purpose of this study was to determine the feasibility of infrared spectroscopy as an alternative method for the prediction of fetal lung development.

STUDY DESIGN

Samples of amniotic fluid were obtained by amniocentesis from 134 patients between the 26th and 41st week of pregnancy. To acquire infrared spectra with a commercial spectrometer, 35 microl of amniotic fluid was required for each spectrum. The lecithin/sphingomyelin ratio was determined separately by thin-layer chromatography for each sample. A robust linear discriminant analysis method was used to partition the samples into normal and abnormal groups according to their infrared spectra. A partial least squares regression analysis was then applied to quantitatively correlate the infrared spectra with the thin-layer chromatography-based lecithin/sphingomyelin ratios.

RESULTS

Qualitatively, the infrared spectra of the amniotic fluid in the validation set were successfully partitioned into lecithin/sphingomyelin <2 and lecithin/sphingomyelin >2 groups. Quantitatively, the lecithin/sphingomyelin ratios predicted from the infrared spectra of amniotic fluid were highly correlated and in excellent agreement with those determined by thin-layer chromatography (correlation coefficient = 0.893).

CONCLUSION

Infrared spectroscopy has the potential to become the clinical method of choice for determining fetal lung surfactant maturity in amniotic fluid.

Prediction of fetal lung maturity from near-infrared spectra of amniotic fluid

OBJECTIVE

The aim of this study was to attempt to correlate the quantitative data obtained from the near-infrared (near-IR) spectra of amniotic fluid with the lecithin/sphingomyelin (L/S) ratio determined from thin layer chromatographic analysis on the same samples, in order to establish the feasibility of near-IR spectroscopy as an alternate method for the prediction of fetal lung development.

METHODS

Samples of amniotic fluid were obtained by amniocentesis from 52 patients between the 26th and 41st week of pregnancy. About 350 microliters of amniotic fluid was required to record the near-IR spectrum over the entire spectral range between 400 and 2500 nm using a commercial spectrometer. The L/S ratio was determined independently by thin layer chromatography (TLC) for each sample. For correlating the infrared spectra with the TLC-based L/S ratios, a partial least squares analysis was used.

RESULTS

The L/S ratios predicted from the near-IR spectra of amniotic fluid were highly correlated and in excellent agreement with those determined by TLC (r = 0.91).

CONCLUSION

Near-IR spectroscopy has the potential to become an alternate method to TLC for prediction of fetal pulmonary maturity.

Prediction of RDS by amniotic fluid analysis: a comparison of the prognostic value of traditional and recent methods

The determination of lecithin or even more the lecithin/sphingomyelin (L/S) ratio in amniotic fluid are both well established in the prediction of neonatal RDS. The immunological measurement of phosphatidylglycerol (PG) and the determination of the surfactant/albumin (S/A) ratio by fluorescence polarization (TDx FLMR) have recently been introduced for the detection of fetal lung maturity. In order to compare traditional versus recent methods L/S ratio and PG determination by one dimensional thin-layer chromatography, enzymatic analysis of lecithin, immunological determination of PG by Amniostat-FLMR and the fluorescence polarization of S/A-ratio by the TDx FLMR were all performed in 141 amniotic fluid samples of 122 patients. Only one out of 72 samples was false negative in the enzymatic lecithin determination (sensitivity 88%). All other methods have a sensitivity and a negative predictive value of 100%. The positive predictive values and the specificity varied between 22%-50% and 58%-87% respectively. The false positive rate, which is high for all methods, is lowest for the L/S ratio. This study demonstrates, that the recent methods are reasonable alternatives in all cases with a positive test. In clinical practice they have the advantage, that the result can be obtained in 15 minutes. If the test is predictive for lung immaturity the L/S ratio should be performed in addition to decrease the false positive rate before any clinical decision is made.

Clinical evaluation of a direct colorimetic method for determination of amniotic phospholipids

Evaluation of amniotic phospholipids, which are a parameter of fetal lung maturation, is important in the management of premature infants. The method available for measuring the lecithin/sphingomyelin (L/S) ratio, which appears to provide an index to fetal lung maturity, is laborious, involving determinations of phospholipids, and so is unsuitable for rapid quantitative measurement of phospholipids in the amniotic fluid in the perinatal period. We developed a simple, sensitive colorimetric assay for phospholipids without their extraction. This assay is based on the fact that phospholipids form stable hydrophobic complexes with Co(SCN)4, Fe(SCN)2- and Fe(SCN)3 within about 1 hr. Amniotic fluid samples (n = 115) were collected from women with normal and abnormal pregnancies in week 16-41 of pregnancy, and these samples were examined both by thin layer chromatography (TLC) and by our method of phospholipid determination. Good correlations were observed between the L/S ratio determined by TLC and the values obtained by this method. Moreover the distributions of the dipalmitoylphosphatidylcholine (DPPC) content and DPPC/sphingomyelin (SM) ratio were similar to those of the PC content and L/S ratio. This method was proved to be more accurate than other methods such as TLC and the shake test for predicting neonatal RDS.

Pulmonary phospholipids in amniotic fluid of pathologic pregnancies: relationship with clinical status of the newborn

We evaluated phospholipids, C-peptide and cortisol levels in amniotic fluid of 203 pathologic pregnancies (63, class A, B and C diabetics; 11 class D, F and H diabetics; 44 preclampsia and 85 Rh-isoimmunization); the control group was 82 normal pregnant women. There was an acceleration of fetal pulmonary maturation in women with preclampsia and severe Rh-isoimmunization in class D, F and H diabetics (at 34 weeks gestation the incidence of mature surfactant (lecithin/sphingomyelin greater than or equal to 2.7 and presence of phosphatidyl-glycerol) in these groups was 30%, 50% and 100%, respectively, while it was zero in the control group). At 37 and 38 weeks only 44.4% of the class A, B and C diabetics had mature surfactant and there was a significant difference with respect to the control group (x2 = 4.9; p less than 0.05); C-peptide levels in these diabetics (class A, B and C) were higher than in controls (p less than 0.001); in pregnant women with accelerated fetal lung maturation they were lower. We demonstrated a close relationship between fetal pulmonary maturity and the type of surfactant in amniotic fluid, which was independent of gestational age.

A rapid electrochemical assay of lecithin in amniotic fluid using a fluoride ion-sensitive electrode

An electrochemical method is described for the determination of lecithin in rat and human amniotic fluid. Choline is released from lecithin enzymatically by phospholipase D and the hydrogen peroxide released by the action of choline oxidase is quantitatively determined by peroxidase-catalyzed rupture of the covalent C-F bond of 4-fluorophenol. The concentration of F- ions in solutions is determined by a fluoride sensitive electrode from the resulting cell potential difference recorded before and 10 min after addition of a solution containing phospholipase D, choline oxidase and horseradish peroxidase. Lecithin levels in rat amniotic fluid increased from about 10 mumol/l on the 20th day of gestation to 80 mumol/l on day 21, which corresponds to the time of spontaneous delivery. In human amniotic fluid the lecithin concentrations determined with this new method parallel those already reported. They were approximately 10 to 50 mumol/l between the 15th and 18th weeks of gestation and increased from 5- to 7-fold between the 37th and 41st weeks of pregnancy. This method was only slightly influenced by the presence of blood or meconium contamination in the amniotic fluid.

Combined enzymatic assay of phosphatidylglycerol and phosphatidylcholine in amniotic fluid

We present here a combined, quantitative enzymatic procedure for determining amniotic fluid phosphatidylglycerol and phosphatidylcholine and relate these findings to the assessment of fetal lung maturity. Under the assay conditions described phospholipase C specifically hydrolyses phosphatidylglycerol (PG) and phosphatidylcholine (PC) but not sphingomyelin, precluding the need for removal of sphingomyelin prior to analysis. Solvent extraction of the phospholipids from the amniotic fluid is, however, employed to avoid spurious elevation of PG and PC results by endogenous glycerol and choline. Of 45 amniocentesis fluids examined, 28 yielded detectable PG concentrations (greater than 0.5 mumol/l) and all but three of these exhibited PC concentrations in excess of 10 mumol/l. One case of respiratory distress occurred in an infant of 29 wk gestation with severe intrauterine growth retardation. Of the remaining 17 fluids in which PG was undetected enzymatically (less than or equal to 0.5 mumol/l), 14 also contained PC concentrations less than or equal to 10 mumol/l and all six cases of true respiratory distress syndrome came from within this sub-group. Strong correlations between the PC concentration and the lecithin:sphingomyelin ratio, r = 0.85 (p less than 0.001) and the PC and PG concentrations, r = 0.96 (p less than 0.001) were also found.

A comparison of AmnioStat-FLM with three established methods of assessing fetal lung maturity

A new rapid test of fetal lung maturity (the AmnioStat-FLM) was compared with two currently available rapid tests and with 2-dimensional thin-layer chromatography (2-d TLC). Forty-nine specimens of liquor obtained within 72 h of delivery were assessed, 27 of which were contaminated with blood or meconium. The AmnioStat-FLM compared well with spectrophotometry, the shake test and with 2-d TLC. Only the Amniostat-FLM and the 2-d TLC were reliable in the presence of contamination. The results suggest that the AmnioStat-FLM is a reliable, rapid test and unaffected by the presence of contamination.

Phosphatidylglycerol and neonatal mortality and morbidity

In spite of major improvements in neonatal intensive care, mortality and morbidity remain a problem for the very preterm baby. In a study of 168 babies born before 36 weeks the presence of phosphatidylglycerol (PG) as a marker of fetal lung maturity in amniotic fluid or pharyngeal aspirate was associated with a lower requirement for ventilatory support and a reduced incidence of intraventricular haemorrhage and patent ductus arteriosus. It is suggested that the value of the antenatal assessment of fetal lung maturity should Perhaps be reviewed since babies in whom PG is absent appear to be at a high risk of sustaining considerable morbidity.

Assessment of the AmnioStat-FLM immunoagglutination test for phosphatidylglycerol in amniotic fluid

One hundred and eight amniotic fluids were assayed by the AmnioStat-FLM (A-FLM) immunological agglutination test for phosphatidylglycerol (PG) and simultaneously measured enzymatically for PG content. Of 52 amniotic fluids found to be PG negative by the A-FLM method, all had enzymatic PG concentrations less than or equal to 1.5 mumol/l. Conversely, of 56 amniotic fluids judged to be either PG positive or weak positive, all but five had enzymatic PG concentrations greater than 1.5 mumol/l. The sensitivity of the A-FLM assay employed clinically for predicting foetal lung maturity was 89% and the specificity was 100%. The overall predictive accuracy of the test could be improved by providing controls at lower, more appropriate PG concentrations. Ninety-one fluids analysed by the A-FLM kit were subsequently tested for the presence of PG by two-dimensional thin-layer chromatography (2D TLC). A 94%-concordance between the methods was found.

Amniotic fluid phosphatidylglycerol and phosphatidylcholine phosphorus as predictors of fetal lung maturity

The contents of phosphatidylglycerol and phosphatidylcholine phosphorus in amniotic fluid (10,000 X g pellets) were studied as predictors of fetal lung maturity. The presence of phosphatidylglycerol predicted the absence of neonatal respiratory distress syndrome with 99% probability. When phosphatidylglycerol was absent, phosphatidylcholine phosphorus was a reliable predictor if measured 3 to 7 days before delivery. The probability that respiratory distress syndrome would not occur was 94% when phosphatidylcholine phosphorus was greater than 6. When measurement was performed within 2 days of delivery, the probability that respiratory distress syndrome would not occur fell to 69%. As measured in amniotic fluid, phosphatidylglycerol and phosphatidylcholine phosphorus are reliable antenatal predictors of fetal pulmonary maturity and, therefore, are useful in the management of a number of obstetric conditions.

Quantitative determination of phosphatidylglycerol in amniotic fluid by enzymatic assay

Phosphatidylglycerol (PG) was extracted from 54 human amniotic fluids for the assessment of fetal lung maturity. The PG values were derived from an enzymatic assay involving initial conversion of PG to glycerol by phospholipase C and alkaline phosphatase with subsequent analysis of the glycerol formed. This method proved to be reliable when compared with a method for two-dimensional thin layer chromatographic (2D TLC) analysis of amniotic fluid phospholipids. The results revealed that in all but one of 27 amniotic fluids in which no PG was detected by 2D TLC, enzymatic PG concentrations were less than or equal to 1.5 mumol/l and out of these, from 10 newborn infants delivered within 72 h of sampling, 4 developed respiratory distress syndrome (RDS). Conversely, in all but one of 27 amniotic fluids found to contain PG by 2D TLC, enzymatic PG concentrations were greater than 1.5 mumol/l and except for one subject from non-identical twins, no infants developed RDS.

Non-specificity of surfactant deficiency in neonatal respiratory disorders

The phospholipid content of lung fluid taken from 77 babies during the first day of life was studied. Babies with hyaline membrane disease had low concentrations of the surfactant phospholipids phosphatidylcholine, phosphatidylinositol, and phosphatidylglycerol. The palmitic acid content in phosphatidylcholine was also lower than normal. Surfactant deficiency was not, however, specific for hyaline membrane disease, as similar phospholipid abnormalities were observed in babies with congenital pneumonia and transient tachypnoea of the newborn. These findings have important clinical implications. They are relevant to research into surfactant substitution and cast doubts on the value of the antenatal phospholipid lung profile of amniotic fluid in predicting the risk of hyaline membrane disease.

Maternal diabetes and neonatal respiratory distress. II. Prediction of fetal lung maturity

Fifty babies were born at less than or equal to 37 weeks to mothers with diabetes. Delivery was undertaken in all patients with the reassurance that the L/S ratio was greater than or equal to 2.0 within the preceding 72 h. Five babies (10%) developed respiratory distress syndrome (RDS). Prediction of fetal lung maturity was improved dramatically by measuring amniotic fluid concentrations of phosphatidylcholine (PC), phosphatidylinositol (PI) and phosphatidylglycerol (PG). Fourteen babies were predicted as having 'no surfactant' (PC less than 20 mg/l, PI less than 2 mg/l and PG less than 2 mg/l), five developed RDS. None of the remaining 36 babies developed the illness: they were predicted as having either 'early surfactant' (PC greater than or equal to 20 mg/l, PI greater than or equal to 2 mg/l but PG less than 2 mg/l) or 'late surfactant' (PC greater than or equal to 20 mg/l, PI greater than or equal to 2 mg/l and PG greater than or equal to 2 mg/l). Measurement of PC levels alone was the most was the most accurate method of predicting RDS. There was a significant association between low surfactant phospholipid concentrations and the development of transient tachypnoea of the newborn.

Amniotic fluid phospholipid profile in multiple pregnancy and the effect of zygosity

Because respiratory distress syndrome (RDS) may occur in one twin but not the other it may be misleading to assess fetal lung maturity using amniotic fluid from only one sac. We compared the amniotic fluid lecithin/sphingomyelin (L/S), phosphatidyl glycerol/sphingomyelin (PG/S) and phosphatidyl inositol/sphingomyelin (PI/S) ratios between co-twins and co-triplets in 32 sets of twins and three set of triplets. In the twin pregnancies we found a weak correlation for L/S ratio but a much improved one for PG/S and PI/S. The concordance between sacs for all three ratios was better in monozygotic than in dizygotic twins. The efficacy of amniotic fluid PG in the determination of fetal lung maturity was demonstrated and the discrepancies between the sacs was much less for PG than for the L/S ratios. Employing the L/S ratio combined with the presence or absence of PG should reduce false results to a minimum.

HPLC of phospholipids in biological fluids -- application to amniotic fluid for the prediction of fetal lung maturity

Because of both the advantage of speed compared with thin layer chromatography (TLC) and the dearth of high pressure liquid chromatography (HPLC) methods for phospholipid separation, it was decided to investigate the use of HPLC with a differential refractometer as detector for the separation and quantitation of amniotic fluid phospholipids required for the prediction of fetal lung maturity. A method was devised which gave results which compared well with those from TLC both in terms of quantitation and predictive value. Despite this, the method was found to lack sufficient reliability for application to the routine clinical assessment of fetal lung maturity. The method does, however, offer a good alternative to two dimensional TLC with phosphate analysis in research work involving quantitation of phosphatidyl inositol, phosphatidyl glycerol and particularly lecithin.

Amniotic fluid phosphatidylglycerol: an early indicator of fetal lung maturity

In a study of 766 amniotic fluids, collected from pregnancies between 26 weeks and term, phosphatidylglycerol (PG) was identified in a greater proportion than was a mature lecithin/sphingomyelin (L/S) ratio at all gestational ages between 28 and 38 weeks regardless of the underlying pregnancy complication. The early appearance of PG was particularly striking in amniotic fluids obtained after preterm rupture of membranes. Since PG has been previously shown to be a useful indicator of the risk of neonatal respiratory distress syndrome, its appearance before a mature L/S ratio suggests that its detection offers a considerable advantage in the management of high-risk obstetric problems in which the earliest possible indication that the fetal lungs are mature is required.