🍬 Fetal Macrosomia Risk Simulator

Maternal Hyperglycemia and Placental Glucose Transfer

Maternal glucose crosses the placenta unchecked, unlike insulin.

• GLUT1: Transfer mechanism (facilitated diffusion)
• ↑↑: Maternal glucose (poor glycemic control)
• None: Insulin crossing (insulin does not cross placenta)
• OGTT: Screening test (oral glucose tolerance test)

Why glucose but not insulin crosses

Placeholder: glucose diffuses via GLUT transporters while maternal insulin cannot cross.

Fetal Pancreatic Beta-Cell Response to Glucose Load

The fetus compensates with its own excess insulin production.

• Hyperplasia: Fetal beta-cells (compensatory growth)
• Anabolic: Insulin effect (growth-promoting hormone)
• 1952: Pedersen hypothesis (glucose-insulin theory)
• Hypoglycemia: Postnatal risk (after cord clamping)

The Pedersen hypothesis

Placeholder: maternal hyperglycemia drives fetal hyperinsulinemia and overgrowth.

Excess Fat Deposition and Fetal Overgrowth

Insulin drives disproportionate fat deposition on the trunk and shoulders.

• >4000g: Macrosomia threshold (birth weight definition)
• Truncal: Fat distribution (shoulders & abdomen)
• Ultrasound: Diagnosis (estimated fetal weight)
• ↑15–45%: Incidence in GDM (vs general population)

Asymmetric fetal overgrowth

Placeholder: diabetic macrosomia concentrates fat on shoulders and trunk, not head.

Shoulder Dystocia — Obstruction of Fetal Shoulders at Delivery

Enlarged shoulders can impact behind the maternal pubic bone.

• Impaction: Dystocia definition (anterior shoulder vs symphysis)
• ↑↑: Risk at >4500g (sharp risk increase)
• McRoberts: Key maneuver (hip flexion technique)
• Brachial plexus: Complication (possible nerve injury)

Recognizing and managing dystocia

Placeholder: shoulder dystocia is an obstetric emergency needing prompt maneuvers.

Weighing Cesarean Delivery Against Dystocia Risk

Clinicians balance surgical risk against the danger of a difficult vaginal birth.

• >4500g: EFW threshold (diabetes) (consider planned cesarean)
• >5000g: EFW threshold (no diabetes) (consider planned cesarean)
• Shared decision: ACOG guidance (individualized counseling)
• ±10–15%: Ultrasound error (EFW estimation limits)

Balancing surgical and dystocia risk

Placeholder: EFW guides but does not mandate the mode of delivery decision.

Placeholder: decisions combine EFW, maternal pelvis, and glycemic history.