Previous studies in pregnant sheep have tested the impact of chronic hyperglycemia on fetal β-cell function, using controlled experimental manipulation of maternal and fetal glucose concentrations and in vivo measurement of fetal insulin secretion to begin to determine mechanisms responsible for the impact of different patterns of maternal and fetal glucose concentration, as occur in diabetic pregnancies, on fetal GSIS [7–11]. This evidence concerns the gene INS and Hyperglycemia.