Diabetes tends to run in families. Because it increases insulin resistance. Hispanic Americans, Native Americans, and African Americans are at increased risk, presumably because compared with whites and Asians, they are statistically more likely to be overweight. Pregnant women produce various hormones essential to the baby's growth. However these hormones may also make it hard for the mother to properly use insulin, causing insulin resistance.
All pregnant women have some degree of insulin resistance.
But if this resistance becomes full-blown gestational diabetes, it usually appears around the 24th week of pregnancy. That's why all pregnant women should be screened for gestational diabetes around that time. Because both gestational and type 2 diabetes develop due to insulin resistance, researchers suspect that these two conditions have a similar genetic basis.