Fetal Implications: Macrosomia and Neonatal Hypoglycemia
The primary concern with GDM is the "Pedersen Hypothesis." Maternal glucose readily crosses the placenta through facilitated diffusion, but maternal insulin does not. When the mother is hyperglycemic, the fetus is also hyperglycemic. In response, the fetal pancreas secretes high levels of its own insulin.
Fetal insulin acts as a potent growth hormone. This leads to Macrosomia (a birth weight over 4,000–4,500 grams). Macrosomic infants often have disproportionate fat deposition around the shoulders, which increases the risk of shoulder dystocia—a birth emergency where the baby's head is delivered, but the shoulders become trapped behind the mother's pelvic bone. Furthermore, once the baby is born and the high-glucose supply from the mother is cut off, the baby’s elevated insulin levels remain, which can cause a dangerous drop in blood sugar known as neonatal hypoglycemia.