Which of the following indicators is performed only on amniotic fluid?

Phosphatidylglycerol (PG) is a specific indicator that is uniquely analyzed in amniotic fluid, primarily used to assess fetal lung maturity. The presence of PG in amniotic fluid is critical because it indicates the production of pulmonary surfactant by the type II alveolar cells of the fetal lungs. This measurement is particularly important in the context of potential preterm birth since adequate levels of surfactant are essential for preventing alveolar collapse and ensuring proper gas exchange after delivery.

In contrast, while Phosphatidylcholine (PC) and Dipalmitoylphosphatidylcholine (DPPC) are also components of surfactant found in amniotic fluid, they are not exclusively measured as indicators specific to amniotic fluid. Furthermore, the Lecithin/Sphingomyelin (L/S) ratio, although it does involve components found in amniotic fluid, is a comparative value rather than a direct indicator solely of amniotic fluid. Thus, PG’s role as an exclusive marker for evaluating the maturity of the fetal lungs in the context of amniotic fluid makes it the correct answer in this scenario.