Which of the following L:S ratios indicates stable surfactant production and mature lungs?

a. 2:1
b. 1:1
c. 1:2
d. 2:3

ANS: A
At approximately 34 to 35 weeks' gestation, this ratio abruptly increases to greater than 2:1. An L:S ratio greater than 2:1 indicates stable surfactant production and mature lungs.