A 33-year-old woman who was 40 lb overweight before pregnancy and has a grandfather with diabetes mellitus (GDM) has developed gestational diabetes

A 33-year-old woman who was 40 lb overweight before pregnancy and has a grandfather with diabetes mellitus (GDM) has developed gestational diabetes. She asks the nurse how she developed this condition because she was healthy before pregnancy and has had an uneventful pregnancy thus far. How could the nurse explain this condition to the woman?