A 32-year-old woman with pre-existing type 2 diabetes mellitus becomes pregnant. She was previously on metformin 1000 mg twice daily and glibenclamide 10 mg daily. At 8 weeks of gestation, she presents for antenatal booking. What is the recommended first-line antidiabetic agent for her pregnancy?
A. Switch to pioglitazone monotherapy
B. Continue metformin; switch glibenclamide to insulin
C. Continue both metformin and glibenclamide as before
D. Insulin monotherapy (discontinue both metformin and glibenclamide)
Explanation
Antidiabetic Management in Pre-Existing Diabetes in Pregnancy
Key Point
In pre-existing diabetes (type 1 or type 2) during pregnancy, insulin is the gold standard. Metformin may be continued, but all oral hypoglycaemic agents (except metformin) must be discontinued and replaced with insulin.
Rationale for Insulin in Pre-Existing Diabetes
1.
Placental Transfer Concerns
Insulin does not cross the placenta → no fetal hyperinsulinemia
Metformin is increasingly accepted in pregnancy (especially in type 2 diabetes) because it does not cause fetal hyperinsulinemia. However, insulin remains the gold standard and is mandatory for type 1 diabetes and for type 2 diabetes when tighter control is needed.
High-YieldNEET PG
The key principle is: Insulin + metformin (if tolerated) is the preferred regimen for pre-existing type 2 diabetes in pregnancy. All other oral agents are discontinued.
Insulin Regimen in Pre-Existing Diabetes
1.
Basal-bolus approach (most common)
NPH insulin for basal coverage (morning and evening)
Rapid-acting insulin (aspart, lispro) before meals
2.
Insulin analogues
Aspart, lispro, glulisine (rapid-acting) — safe in pregnancy
Detemir, glargine (long-acting) — increasingly used; safe data
3.
Monitoring
Fasting and pre-meal blood glucose targets: 70–100 mg/dL
2-hour postprandial target: <120 mg/dL
HbA1c target: <6.5% (if safe to achieve)
Warning
Aggressive insulin therapy in early pregnancy increases hypoglycaemia risk. Dose reduction of 15–20% is often needed in first trimester due to improved insulin sensitivity.
Why Option 0 Is Correct
Metformin continuation is acceptable (emerging evidence of safety; does not cross placenta significantly)
Glibenclamide discontinuation is mandatory (crosses placenta; causes fetal hyperinsulinemia)
Insulin initiation is required (gold standard for pre-existing diabetes in pregnancy)
ACOG Practice Bulletin 190; ADA Standards of Care in Diabetes 2023
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