Inpatient Obstetric Nurse (NCC) Practice Exam

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The lab test used to determine fetal lung maturity is called what?

L/S ratio
Beta-HCG ratio
PG ratio
Alpha-fetoprotein ratio

The correct answer is: L/S ratio

The lab test used to determine fetal lung maturity is the Lecithin/Sphingomyelin (L/S) ratio. This test measures the amount of lecithin and sphingomyelin, two phospholipids found in amniotic fluid. Lecithin is produced by the mature type II alveolar cells in the lungs and increases as gestation progresses, while sphingomyelin levels do not significantly change. A higher L/S ratio indicates greater lung maturity and a lower risk of respiratory distress syndrome in the newborn, as sufficient amounts of surfactant are required for lung function at birth. In contrast, the other options provided do not directly assess lung maturity. The beta-HCG ratio relates to pregnancy hormone levels and is used to evaluate various pregnancy-related conditions. The PG (phosphatidylglycerol) ratio can provide additional information about fetal lung development but is not the primary assessment. Alpha-fetoprotein levels are used to screen for certain fetal abnormalities but do not indicate lung maturity. Thus, the L/S ratio remains the standard and most relevant test for determining fetal lung maturity.