Gestational diabetes is a form of diabetes that develops during pregnancy and usually disappears after giving birth. It occurs most commonly during the second and third trimesters and is caused by hormones from the placenta that make the mother less sensitive to insulin. Gestational diabetes increases risks for both mother and baby if not treated, such as large baby size, premature delivery, and increased cesarean delivery rates. It is diagnosed through blood tests and treated initially through medical nutrition therapy, exercise, and sometimes medications like insulin if needed to control blood sugar levels.