What are other Names for this Test? (Equivalent Terms)
- L/S Ratio Amniotic Fluid Test
What is Lecithin/Sphingomyelin Ratio Amniotic Fluid Test?
- The ratio of lecithin to sphingomyelin is used as a measure of the health of a growing fetus
- Lecithin is a type of fat produced by the body to lubricate the tiny cells of the lungs, called the alveoli
- Sphingomyelin is also a type of fat. It is valuable for testing purposes, because it is produced by the developing fetus at a constant rate during pregnancy
- Measuring the amount of lecithin relative to the amount of sphingomyelin in a fetus gives information about the maturation of the fetus and the potential for having hyaline membrane disease
- Normally, lecithin significantly increases after week 35 of pregnancy. Because sphingomyelin remains constant, this should translate to an increase in the lecithin/sphingomyelin (L/S) ratio. If the ratio is not around 3 or 4 by week 35 of pregnancy, there is a danger of alveolar collapse, and thus lung collapse (or atelectasis) because of lecithin deficiency
- The Lecithin/Sphingomyelin Ratio Amniotic Fluid Test determines the L/S ratio in a fetus. It is used to determine fetal maturity and assess the risk of a respiratory syndrome upon delivering the baby
What are the Clinical Indications for performing the Lecithin/Sphingomyelin Ratio Amniotic Fluid Test?
Following are the clinical indications for performing the Lecithin/Sphingomyelin Ratio Amniotic Fluid Test:
- Uncertain gestation period
- Determining the risk of neonatal respiratory distress syndrome prior to delivery
How is the Specimen Collected for Lecithin/Sphingomyelin Ratio Amniotic Fluid Test?
Following is the specimen collection process for Lecithin/Sphingomyelin Ratio Amniotic Fluid Test:
Sample required: Amniotic fluid
Process of obtaining an amniotic fluid sample (amniocentesis):
- A local anesthetic is applied to the site of amniocentesis
- A needle is inserted into the pregnant woman’s abdominal wall, through the uterus and into the amniotic sac
- An ultrasound scan is used to guide the needle, as it punctures the sac away from where the baby is located
- Approximately 20 mL of amniotic fluid is obtained and the needle withdrawn
Preparation required: No special preparation is needed prior to the test.
What is the Significance of the Lecithin/Sphingomyelin Ratio Amniotic Fluid Test Result?
Interpretations of the Lecithin/Sphingomyelin Ratio Amniotic Fluid Test value depend on how far the pregnancy has progressed.
- A low value (less than 4:1, or 15-21 mg/dL for lecithin and 4-6 mg/dL for sphingomyelin) after week 35 of pregnancy may point to a possible hyaline membrane disease prior to delivery
- A lowered test value may indicate that the fetal lungs are not probably ready to breathe on its own. This may also predispose the newborn to breathing difficulties necessitating intense medical attention at birth
The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.
Additional and Relevant Useful Information:
- No single test is available to determine fetal distress. The Lecithin/Sphingomyelin Ratio Amniotic Fluid Test is just one of several tests, including the amniotic fluid index, used for this purpose
Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.
The following DoveMed website link is a useful resource for additional information:
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