Some people strongly believe that diabetes is associated with an increased risk of miscarriage. However, this has not been conclusively demonstrated. Just as with SLE (systemic lupus erythematosus), if the illness is controlled the miscarriage rate dose not go up. Most of the studies reporting such a link were from the 1960s, when diabetes control was not as efficient as it is today.

There is definitely no increase in miscarriages in gestational diabetes, that is, in patients who have diabetes only when pregnant (which has resulted from pregnancy hormones interfering with the action of insulin). But some studies have shown slightly increased miscarriage rates in frank diabetes, that is, in insulin-treated diabetics who become pregnant. However, even then it is avoidable, and there is no real difference between this group and nondiabetic women who become pregnant. A glucose-tolerance test, in which glucose is given as a drink, is and the blood is tested for up to there hours after the drink, is therefore not necessary as part of a routine workup in recurrent miscarriage. Rates of miscarriage seem only to increase in uncontrolled diabetes.