The nurse knows that a lecithin/sphingomyelin (L/S) ratio finding of 2:1 on amniotic fluid means: ...

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Rationale 1: Early in pregnancy, the sphingomyelin concentration in amniotic fluid is greater than the concentration of lecithin, and so the L/S ratio is low if the fetus's lungs are immature, which is not the case in this instance.
Rationale 2: The L/S ratio isn't a measurement for congenital anomalies or size of the fetus.
Rationale 3: A 2:1 L/S ratio indicates that the risk of respiratory distress syndrome (RDS) is very low and that the fetus's lungs are mature.
Rationale 4: The L/S ratio isn't a measurement for congenital anomalies or size of the fetus.