With diabetes, your body either doesn't make enough insulin or can't use its own insulin as well as it should.  This causes sugars to build up in your blood. Type 1 diabetes is generally caused by an autoimmune reaction where the body's defense system attacks insulin-producing cells in the pancreas. In type 2 diabetes, the body is able to produce insulin, but it is either not sufficient or the body doesn't respond to it. Gestational diabetes sometimes develops in pregnant women.