The largest and most robustly designed of these studies showed no significant difference in the basal PRL levels of T1DM patients during lactation at days 3, 14, or 42 postpartum when compared with either matched non-diabetic controls or healthy non-diabetic reference women, but did show that day 42 maternal serum PRL was lower in a subset of T1DM patients with longer-standing and/or more complicated disease. This evidence concerns the gene PRL and type 1 diabetes mellitus.