INS and obesity due to melanocortin 4 receptor deficiency: The findings of the highest HOMA-IR in group 2 GDM, the lowest HOMA-β in group 3 GDM, and both high HOMA-IR and low HOMA-β in group 4 GDM suggest that the highest prevalence of GDM in the old and obese group 4 is the additive result of increased insulin resistance due to obesity and decreased insulin secretion due to age [55].