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Meconium has no lecithin or sphingomyelin but affects the lecithin/sphingomyelin ratio
S A Longo1, C V Towers, A Strauss
1Department of Obstetrics and Gynecology, Women's Hospital, Long Beach Memorial Medical Center, Long Beach, CA, USA.
Objective:
Although a few studies have evaluated the effect of meconium on the lecithin/sphingomyelin ratio for testing of fetal lung maturity, to date these studies have assessed only the lecithin-sphingomyelin ratio of amniotic fluid contaminated with meconium. The purpose of this study was (1) to determine whether meconium by itself has a lecithin/sphingomyelin ratio and, if so, (2) to determine whether the lecithin/sphingomyelin ratio is constant.
Study Design:
A lecithin/sphingomyelin ratio was obtained by standard thin-layer chromatography on the first meconium stool of 20 neonates between 31 weeks and term. A quantitative assay was then performed on a sample from each gestational age (7 samples ranging from 31 weeks to term) to confirm the presence of lecithin and sphingomyelin.
Results:
The 20 samples had atypical thin-layer chromatographic migratory patterns in the zones for lecithin and sphingomyelin. The presumed lecithin/sphingomyelin ratios ranged from 1.1 to 3.6, with no correlation with gestational age. However, the quantitative assay did not detect the presence of lecithin or sphingomyelin in any of the analyzed samples.
Conclusions:
Meconium does not appear to contain lecithin or sphingomyelin but has an unidentified moiety whose migratory pattern, as shown by qualitative standard thin-layer chromatography, is similar to that of lecithin with sphingomyelin. Therefore the presence of meconium in amniotic fluid may falsely raise or lower the lecithin/sphingomyelin ratio and confuse fetal lung maturity interpretations.
Insights
Meconium does not contain lecithin or sphingomyelin, despite appearing to have a lecithin/sphingomyelin ratio. This finding may impact fetal lung maturity testing accuracy.
Area of Science:
- Neonatal Physiology
- Biochemistry
- Obstetrics
Background:
- The lecithin/sphingomyelin ratio in amniotic fluid is a key indicator of fetal lung maturity.
- Previous studies have examined meconium's effect on this ratio in amniotic fluid.
- However, the intrinsic properties of meconium itself regarding this ratio have not been thoroughly investigated.
Purpose of the Study:
- To determine if meconium possesses its own lecithin/sphingomyelin ratio.
- To ascertain if any such ratio in meconium is consistent across different gestational ages.
Main Methods:
- Standard thin-layer chromatography was used to analyze the first meconium stool from 20 neonates (31 weeks to term).
- A quantitative assay was performed on samples from 7 gestational ages to confirm the presence of lecithin and sphingomyelin.
Main Results:
- Qualitative analysis showed atypical chromatographic patterns for lecithin and sphingomyelin in meconium samples.
- Presumed lecithin/sphingomyelin ratios varied from 1.1 to 3.6, without correlation to gestational age.
- Quantitative assays failed to detect lecithin or sphingomyelin in any meconium sample.
Conclusions:
- Meconium lacks detectable lecithin and sphingomyelin.
- An unidentified substance in meconium mimics the chromatographic behavior of lecithin and sphingomyelin.
- The presence of meconium can lead to inaccurate fetal lung maturity test results by altering the lecithin/sphingomyelin ratio.