As it grows, the placenta secretes hormones that make it harder for a woman's body to use insulin normally, to turn glucose in the blood into fuel for the cells. Thus, the mother needs an increasingly large amount of insulin to maintain normal blood glucose levels. When the mother's pancreas can't keep up with the higher demand for insulin, the body falls behind in processing glucose, and gestational diabetes results.

If not controlled, the excess glucose in the blood can pass into the baby's blood; the baby matches the increase in glucose by ramping up its own insulin production and the energy is stored as fat. Large babies can lead to difficult deliveries. In addition, the baby's overproduction of insulin may increase his or her eventual risk of obesity and type 2 diabetes.