A surrogate marker with a threshold of 70 mg/g that would predict pulmonary maturity is the which of the following?

• A. Surfactant/albumin ratio of 70 mg/g
• B. Phosphatidylglycerol
• C. Lecithin/sphingomyelin ratio
• D. Alpha-fetoprotein

Answer: (A)

Pulmonary maturity is assessed by markers in amniotic fluid that reflect surfactant production by the fetal lungs. The surfactant/albumin ratio compares how much surfactant is present relative to albumin in the fluid. As the fetal lungs mature, surfactant output increases, so the ratio rises. A threshold around 70 mg of surfactant per gram of albumin indicates maturity and is associated with a lower risk of respiratory distress syndrome after birth. Other markers exist—phosphatidylglycerol and the lecithin/sphingomyelin ratio are also used to gauge maturity—but the specific surrogate described with a 70 mg/g threshold is the surfactant/albumin ratio. Alpha-fetoprotein is not used to assess lung maturity.