Abstract Objective: To compare the effectivity of N-acetylcysteine with Be¬tamethasone in fetal lung maturation. Methods: This research was a double blind randomized clinical tri¬als in women threatened by preterm delivery (28 to 34 weeks of gestation). Results: There were 90 subjects randomly assigned to N-acetylcys¬teine group (n=30), betamethasone group (n=30), and the control grou…