Gestational Diabetes Management
A 22-year-old primigravida at 33 weeks of gestation is diagnosed with gestational diabetes after a 75 g oral glucose tolerance test showing a fasting glucose of 5.4 mmol/L and a 2-hour value of 9.1 mmol/L. She has no symptoms and fetal growth is on the 60th centile. Which of the following is the most appropriate first-line therapy?
- A.Oral metformin
- B.Dietary therapy and exerciseCorrect
- C.Subcutaneous insulin
- D.Intravenous insulin infusion
Explanation
First-line treatment of gestational diabetes is medical nutrition therapy combined with physical activity, and this alone achieves glycaemic targets in about 70 to 85 percent of women. The dietary prescription distributes carbohydrate across three meals and two to three snacks, favours low glycaemic index sources, and avoids the ketosis of excessive restriction; 30 minutes of moderate activity such as walking on most days improves peripheral insulin sensitivity. Women are taught capillary glucose self-monitoring with usual targets of fasting below 5.3 mmol/L and 1-hour postprandial below 7.8 mmol/L or 2-hour below 6.7 mmol/L. Pharmacotherapy is added only if these targets are not met after roughly 1 to 2 weeks of dietary therapy, or immediately if fasting glucose is markedly elevated or the fetus is already macrosomic with polyhydramnios. Insulin is the preferred pharmacological agent because it does not cross the placenta; metformin is an accepted alternative in many guidelines but does cross the placenta and up to half of women eventually need supplemental insulin. Intravenous insulin is reserved for labour, diabetic ketoacidosis or perioperative care. Postpartum, a 75 g oral glucose tolerance test is repeated at 6 to 12 weeks because of the high lifetime risk of type 2 diabetes.
Why each option
- A.
- Metformin is an option when dietary measures fail, but it is not started before a trial of nutrition therapy in an asymptomatic woman with a normally grown fetus.
- B.
- Correct. Medical nutrition therapy with exercise is first-line and controls the majority of cases of gestational diabetes.
- C.
- Subcutaneous insulin is the preferred drug once diet fails or when hyperglycaemia is severe, not as initial therapy here.
- D.
- Intravenous insulin is used for diabetic ketoacidosis, labour or surgery, not for routine outpatient gestational diabetes.
Reference: ADA Standards of Care in Diabetes 2025, Management of Diabetes in Pregnancy; ACOG Practice Bulletin 190, Gestational Diabetes Mellitus
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