Inpatient Obstetric Nurse (NCC) Practice Exam 2026 - Free NCC Practice Questions and Study Guide

The definitive indication of fetal lung maturity is demonstrated by an L/S (lecithin/sphingomyelin) ratio greater than 2:1. This ratio is essential in assessing the maturity of the fetal lungs, particularly in the context of preterm labor and the risk of respiratory distress syndrome (RDS) in newborns.

Lecithin is a phospholipid that is produced by the type II alveolar cells in the lungs and is a major component of surfactant, which reduces surface tension in the alveoli, facilitating proper lung inflation and function at birth. Sphingomyelin, on the other hand, is produced in the fetal lung before the production of lecithin increases significantly.

As the fetus develops, especially around the 34th to 36th week of gestation, the production of lecithin increases, leading to a higher ratio of lecithin to sphingomyelin. A ratio greater than 2:1 indicates that there is sufficient surfactant present, suggesting that the fetal lungs are mature and the risk of RDS is considerably lower. This is crucial for clinical decision-making, particularly when considering the timing of delivery and potential interventions to support fetal lung function.

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