Maternal hyperglycemia can cause macrosomia through which mechanism?

• A. Hyperinsulinemia stimulates growth
• B. Hypoglycemia causes growth
• C. Insulin deficiency causes growth
• D. Glucose does not cross the placenta

Answer: (A)

Maternal high blood glucose raises the amount of glucose crossing the placenta into the fetus, causing fetal hyperglycemia. In response, the fetal pancreas ramps up insulin production (hyperinsulinemia). Insulin acts as a powerful growth hormone for the fetus, promoting protein synthesis and fat deposition, which leads to increased fetal growth and macrosomia. After birth, the newborn may experience hypoglycemia because the high insulin level persists briefly even though the maternal glucose supply has stopped.

Why the other ideas don’t fit: glucose does cross the placenta, so the notion that placental glucose transfer is blocked isn’t correct; macrosomia isn’t driven by insulin deficiency or fetal hypoglycemia, but by excess fetal insulin stimulating growth.