Diabetic ketoacidosis (DKA) during pregnancy is a serious complication in both mother and fetus. Most incidences occur during late pregnancy in women with type 1 diabetes mellitus. We report the rare case of a woman with type 1 diabetes mellitus who had normal glucose tolerance during the first trimester but developed DKA during late pregnancy. Although she had initially tested positive for screening of gestational diabetes mellitus during the first trimester, subsequent diagnostic 75-g oral glucose tolerance tests showed normal glucose tolerance. She developed DKA with severe general fatigue in late pregnancy. The patient's general condition improved after treatment for ketoacidosis, and she vaginally delivered a healthy infant at term. The presence of DKA caused by the onset of diabetes should be considered, even if the patient shows normal glucose tolerance during the first trimester.
Learning points: The presence of DKA caused by the onset of diabetes should be considered, even if the patient shows normal glucose tolerance during the first trimester.Symptoms including severe general fatigue, nausea, and weight loss are important signs to suspect DKA. Findings such as Kussmaul breathing with ketotic odor are also typical.Urinary test, atrial gas analysis, and anion gap are important. If pH shows normal value, calculation of anion gap is important. If the value of anion gap is more than 12, a practitioner should consider the presence of metabolic acidosis.