CLINICAL FOLLOW-UP QUESTION:

Use the clinical case information below to determine the appropriate next evaluation.

A 20-year-old woman (G1P0) presents at 10 weeks’ gestation after being referred by her obstetrician. She has a normal menstrual cycle history, had no difficulty conceiving, and has an otherwise unremarkable medical history. She is not taking any medications except a prenatal vitamin. Her family history is notable for diabetes mellitus in her father and several uncles and aunts, but she does not know which type it is. On physical examination, her BMI is 21 kg/m2. Her examination findings are unremarkable.

Laboratory test results obtained at her obstetrics visit:

• Fasting plasma glucose = 115 mg/dL (70-99 mg/dL) (SI: 6.4 mmol/L [3.9-5.5 mmol/L])
• Hemoglobin A1c = 6.7% (4.0%-5.6%) (50 mmol/mol [20-38 mmol/mol])

On the basis of the presented information, which of the following is the most likely underlying etiology of her diabetes?