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You are watching: Lecithin/sphingomyelin (l/s) ratio

StatPearls . Endowment Island (FL): StatPearls Publishing; 2021 Jan-.


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Introduction

The Lecithin-to-Sphingomyelin ratio (L/S ratio) is one of several techniques for clinicians to assess fetal lung maturation. This biochemical check was very first introduced in the 1970s, where a sample that amniotic fluid was accumulated via amniocentesis to determine the risk of the neonate occurring respiratory distress syndrome (RDS). The sample to be then evaluated, using thin-layer color layer analyzer to evaluate the size of lecithin loved one to sphingomyelin.<1> Historically, this test was helpful for clinicians to attempt to time the distribution of babies prior to 39 weeks gestation in wishes of minimization the RDS. In recent years, the check has had actually a decrease in use because of guidelines and also recommendations from major medical societies.<2>

Fetal lung breakthrough occurs as a gradual process in i m sorry the mature of the pulmonary mechanism progresses with increasing gestational age. Over there are 5 stages that lung development, provided in sequential order: embryonic (3 to 7 weeks), pseudo glandular (5 to 17 weeks), canalicular (16 to 26 weeks), saccular (26 to 36 weeks), and also alveolar (32 weeks with childhood). The significant maturation that the fetal lungs occurs throughout the alveolar stage when the tires of type II pneumocytes occurs. Type II pneumocytes room responsible for the manufacturing of surfactant, i beg your pardon is crucial for the support of alveoli in the lung to combat surface ar tension.

The impact of the surfactant stays clear of the fallen of the alveoli during expiration. The ingredient of the surfactant has phospholipids, proteins, and lipids. Of noteworthy importance is the ingredient of the phospholipids. Phosphatidylcholine, also referred to together lecithin, is one of the phospholipids existing in maturation surfactant. It is stored and also secreted by organelles called lamellar bodies.<3> 

These organelles appear after 22 come 24 main gestation.  before the 28th mainly of gestation, the fetal lung mostly synthesizes sphingomyelin, a nonpulmonary lipid. At about 32 mainly gestation, the number of lamellar bodies increases, which converts into enhanced surfactant present in the fetal lungs and also amniotic fluid. At this point in lung maturity, the ratio of lecithin and sphingomyelin are relatively equal in concentration. By 35 main of gestation, the mature surfactant has been produced and also is marked by a sharp increase in the concentration the lecithin in the fetal lungs and amniotic fluid. The lecithin come sphingomyelin proportion of 2:1 or better is characteristics of mature fetal lungs. Fetuses yielded prior come this gestational period are at enhanced risk that neonatal respiratory tract distress syndrome.  


Specimen Collection

Obtaining a sample the amniotic liquid can occur via amniocentesis after 34 weeks of gestation or from vaginal pooling in the preterm premature rupture of membranes (PPROM). In the instance of amniocentesis, one ultrasound is used to determine an adequately sized pocket that amniotic liquid that is away from the fetus. Local anesthesia have the right to be provided for the sampling site. A stylet is presented through the abdomen under ultrasound guidance, and also a syringe is fastened to acquire the sample. In the situation of PPROM, the sample can be built up from the vagina. However, if blood were to be present within the sample or in the vagina, the results of the L/S ratio would be invalidated. 


Procedures

A slim layer chromatography is carry out on the sample, which deserve to determine the ratio of lecithin to sphingomyelin in the amniotic fluid.<4>


Indications

Historically, indications for amniocentesis because that fetal lung maturity contained maternal comorbidities, uterine and placental complications, and also obstetric concerns. Some of these conditions included diabetes, chronic hypertension, preeclampsia, placenta previa, preterm labor, preterm premature rupture of the membranes, fetal heart rate abnormalities, and also several various other concerns. Based on brand-new guidelines, this indications no longer warrant trial and error the L/S proportion or performing other fetal lung experimentation modalities. One feasible exception relates to inaccurate date of the gestational age. If over there is bad dating the the pregnancy and also the distribution is to it is in planned between 32 come 39 mainly gestation, the clinician may think about testing because that fetal lung maturity.<5>


Potential Diagnosis

The main emphasis of trial and error the L/S proportion is to determine fetal lung maturity in an effort to to decrease the threat of moving a neonate with respiratory distress syndrome (RDS). RDS predominantly occurs in preterm babies less 보다 39 mainly gestation with raised risk through lesser gestational age. 


Normal and an essential Findings

The typical L/S proportion is 2.0 to 2.5 and is far-reaching for appropriate fetal lung development. An L/S ratio of much less than 2.0 is far-ranging for immature fetal lung development. Because that patients who have poorly regulated diabetes, there to be a discussion for the L/S ratio to it is in 3.0 as result of elevated maternal glucose impacting the maturity of the emerging fetal lungs. However, it was later discovered that there was no significant difference in the L/S ratio between diabetic and non-diabetic patients.<6> Some institutions use 3.0 together the cutoff because that pregnancies through poorly managed diabetes. 


Interfering Factors

The existence of meconium and also blood in the sample can transform the result of the L/S ratio. The existence of meconium in the sample deserve to invalidate the last result.<7> The presence of blood can decrease the an outcome of the L/S ratio causing alterations in the interpretation of the test. If a an outcome of the L/S proportion were to be read initially as less than 2.0, the presence of blood would further decrease the value obtained, resulting in an interpretation as an immature result. Top top the other hand, if the result were come be check out as more significant than 2.0, in the visibility of blood, the sample would still be lead to the interpretation as mature regardless of the decrease in the value.<8>


Complications

Major symptom of delivery of a neonate before 39 weeks gestation have concentrated on the aftermath of incomplete pulmonary advancement such together respiratory distress syndrome, bronchopulmonary dysplasia, pulmonary hypertension, and the need for respiratory tract support.<9>


Patient Safety and also Education

Risks of performing one amniocentesis because that determining one L/S proportion are rare yet include maternal sepsis, intrauterine rupture, maternal-fetal hemorrhage, and also fetal heart price abnormalities.<5>


Clinical Significance

The L/S ratio was a test offered to help guide clinicians in identify the timing of delivery of neonates to minimization the risk of emerging respiratory distress syndrome.

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<10> The evidence of immature fetal lung by this biochemical test had actually been supplied to support the administration of glucocorticoids for fostering lung maturation. Other fetal lung maturity testing alternatives have been arisen since the introduction of the L/S ratio. They encompass lamellar body count, phosphatidylglycerol check (PG), foam stability test, and surfactant/albumin ratio. Over the last several years, the should test for fetal lung maturity has actually diminished. In many circumstances, if over there is a maternal or fetal indication to deliver before term, performing one L/S proportion test would certainly not it is in necessary. 


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