In amniotic fluid contaminated with blood or meconium, which test demonstrates greatest validity for fetal lung maturity?

• A. Phosphatidylglycerol (PG)
• B. Lamellar body count (LBC)
• C. Lecithin/sphingomyelin (L/S) ratio
• D. Surfactant/albumin ratio

Answer: (A)

Assessing fetal lung maturity hinges on markers in amniotic fluid that reflect surfactant production by the fetal lungs. When the sample is contaminated with blood or meconium, some traditional tests lose reliability. Phosphatidylglycerol (PG) stands out because its appearance in amniotic fluid tracks lung maturity and its detection is relatively unaffected by such contaminants. A positive PG result strongly correlates with adequate surfactant production and lowers the risk of neonatal respiratory distress syndrome, making it a robust choice in contaminated samples.

Lecithin–sphingomyelin (L/S) ratio can be influenced by contaminants, and its accuracy diminishes when meconium or blood is present, so it’s less reliable in these scenarios. Lamellar body counts can vary with sample handling and aren’t as consistently predictive across different lab methods. Surfactant–albumin ratio can be confounded by the presence of albumin from blood and is less specific for surfactant maturity.