A pregnant woman at 32 weeks of gestation was emergently admitted to our hospital with symptoms of nausea, vomiting, and uterine contraction. Cardiotocogram demonstrated a loss of variability and late deceleration in fetal heart rate pattern. Emergency cesarean section was performed, and a male infant weighing 1750 g was born with Apgar scores of 1 at 1 min, and 3 at 5 min after delivery. After cesarean section, the patient developed an acetone breath odor, and blood examination demonstrated remarkable acidemia and an extremely high level of blood glucose. The patient was diagnosed with ketoacidosis with acute onset of fulminant type 1 diabetes mellitus. Intensive care was applied due to the severe diabetes mellitus conditions. The patient's general condition ameliorated during the postoperative period, although there was a possibility of neurological complications in the infant.