Only in normal pregnancy does the lecithin/sphingomyelin (L/S) ratio correlate with gestational age. Abnormalities of pregnancy, including maternal, fetal, and placental conditions, may affect markedly the maturation of the fetal lung. Certain conditions associated, e.g., with maternal hypertension and severe placental problems including retroplacental bleeding and ruptured membranes accelerate L/S ratio maturation and other conditions such as diabetes mellitus (A, B, and C) delay maturation of the L/S ratio. These studies suggest that an association exists between general major organ system maturation of the fetus—“functional maturity”-and the L/S ratio, independent of gestational age or birth weight.