Preterm labor or premature rupture of membranes is one of the major complications of twin pregnancies and contributes to the increased maternal and perinatal morbidity and mortality. Forty-seven twin pregnancies and a comparable group of singleton pregnancies constitute the study population. These patients' pregnancies were complicated only by preterm labor. The lecithin to sphingomyelin ratio is used as an index of fetal lung maturation. Analysis of the data reveals that fetal lung maturation is biochemically comparable between twin and singleton pregnancies and among twins for a given gestational age in this clinical setting.