In pregnancies affected by diabetes, what L/S ratio cutoff may be considered to predict lung maturity given the risk of RDS even with L/S 2:1?

• A. 3:1
• B. 2:1
• C. 4:1
• D. 1:1

Answer: (A)

In pregnancies affected by diabetes, fetal lung maturation can be delayed because maternal hyperinsulinemia bluntly inhibits surfactant production. Since the L/S ratio rises with maturation, a higher ratio is needed before we can be confident the lungs are mature. That’s why a 3:1 cutoff is used to predict maturity in diabetic pregnancies—the traditional 2:1 threshold may still leave the infant at risk for respiratory distress syndrome, whereas 3:1 provides a more reliable signal of matureness in this context. A 4:1 cutoff would be overly conservative and could delay necessary delivery, while a 1:1 ratio is clearly insufficient to indicate maturity.