A 28-year-old with Type 1 diabetes mellitus (pre-gestational) presents at 8 weeks gestation. HbA1c is 9.2%. She is on insulin. What is the MOST important counselling point regarding the risk to the fetus specifically related to this HbA1c level?

• A Increased risk of macrosomia in the third trimester due to fetal hyperinsulinaemia
• B Risk of stillbirth is the primary concern in the first trimester
• C HbA1c 9.2% increases risk of preterm labour but not congenital anomalies
• D Increased risk of major congenital malformations, particularly cardiac and neural tube defects, due to poor glycaemic control during organogenesis ✓

Explanation

Periconceptional hyperglycaemia (elevated HbA1c at the time of conception and early first trimester) is associated with a significantly increased risk of major congenital malformations, especially cardiac defects (ventricular septal defect, transposition of great arteries) and neural tube defects, as organogenesis occurs during weeks 4–8. An HbA1c of 9.2% carries an approximately 4–8 times higher malformation risk compared to general population. Macrosomia is a third-trimester complication of ongoing poor control. This is why preconceptional optimisation (target HbA1c < 6.5%) is critical.

Reference: Williams Obstetrics, 26th ed.

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Written and medically reviewed by the StethoPrep medical team.