We studied fetal lung maturity (FLM) by the amniotic fluid surfactant/albumin (FLM S/A) ratio and the disaturated phosphatidylcholine (DSPC) amniotic fluid levels at different gestational ages in diabetic (179 women with type 1 diabetes mellitus antedating pregnancy; infants delivered within 72 hours after amniotic fluid testing for DSPC level and FLM S/A ratio) and nondiabetic pregnancies (2 independent nondiabetic groups, 300 for FLM S/A ratio and 1,231 for DSPC level). The degree of maternal glycemia during gestation was estimated by serial measurements of hemoglobin A1. Multiple regression analyses, including gestational age (GAs) and diabetic status as independent variables and FLM S/A ratio and DSPC level as dependent variables, revealed significant effect from diabetic status and GA for FLM S/A ratio and a significant effect from GA but not from diabetic status for DSPC level. Glucose levels were controlled adequately throughout gestation as reflected by mean total glycated hemoglobin levels. Amniotic fluid levels of DSPC, the major surface tension-lowering component of pulmonary surfactant, are not significantly different between diabetic and nondiabetic pregnancies at different GAs.