There are ethnic differences in insulin secretion and resistance in healthy nondiabetic adults, children, and adolescents. It is not known whether these ethnic differences are also detectable during normal pregnancy. The objective of this study was to examine whether ethnic differences in glucose homeostasis (C-peptide/insulin/glucose dynamics) are present in nondiabetic pregnant women. Fasting serum C-peptide, insulin, and plasma glucose were measured in the second and third trimesters in 773 pregnant women (343 African-Americans, 312 Hispanics, and 118 Caucasians), and a 50-g oral glucose challenge test was performed in the third trimester. Significantly reduced C-peptide levels and C-peptide to insulin ratio and elevated fasting insulin to glucose ratios were observed in African-American women compared with Caucasians and/or Hispanics. Similar results were found after a 50-g glucose load. In addition, African-Americans had greater insulin and lower glucose levels at glucose challenge test. There were ethnic differences in insulin production and resistance in both fasting and glucose-stimulated conditions in normal young nondiabetic pregnant women.