Low blood sugar (hypoglycemia)
Tight blood sugar control can improve your chances of having a healthy pregnancy, but tight control also puts you at risk of low blood sugar. Your body gets used to your blood sugar being between a certain, narrow range. When your blood sugar drops below that range, your body, in a sense, overreacts, causing harmful side effects.

High blood sugar (hyperglycemia)
High blood sugar, another potential problem of tight control, can occur if your body doesn't have enough insulin, you overeat or you exercise less than you planned. Stress or illness, such as a cold or influenza, also may cause high blood sugar.

Diabetic ketoacidosis (DKA)
Diabetic ketoacidosis is another condition to be aware of. It's caused by increased levels of ketones, a blood acid your body produces when your cells lack insulin and are unable to use glucose, and your body begins to break down fat for energy. Ketones, a byproduct of fat metabolism, can build up in your blood and endanger your health and that of your baby.