Final answer:
The L/S ratio that indicates fetal lung maturity is approximately 2.5, with a ratio of less than 1.5 posing a high risk for infant respiratory distress syndrome. From week 24 until term, the respiratory system undergoes significant growth, and by week 28, a baby may breathe on its own if born prematurely.
Step-by-step explanation:
The lecithin/sphingomyelin (L/S) ratio is used to assess fetal lung maturity. A ratio of approximately 2.5 indicates mature lungs, while a ratio between 2.4 to 1.6 suggests a low risk, and a ratio less than 1.5 indicates a high risk of infant respiratory distress syndrome. The development of the respiratory system, including the production of pulmonary surfactant, is crucial for ensuring that a new-born can breathe properly post-birth, with significant development occurring from week 24 until term. A marker of adequate respiratory development is reached around week 28, when enough alveolar precursors have matured, though full lung maturity continues into childhood. In cases of premature birth, treatment to aid lung development may involve administering steroids to the mother or infant and the application of surfactants, as well as mechanical ventilation to facilitate breathing.