There are three main types of diabetes: type 1, type 2, and gestational diabetes mellitus. 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 does not respond to it. Gestational diabetes sometimes develops in pregnant women when the body is unable to make and use enough insulin needed for pregnancy. There are other types of diabetes which are less common but equally serious.