**Core Concept**
The neonatal complications of a fetus in a diabetic mother are primarily related to the effects of excess glucose on fetal metabolism, leading to an increased risk of hypoglycemia, polycythemia, and hypocalcemia. These complications arise due to the fetal pancreas's inability to produce sufficient insulin in response to the high glucose levels.

**Why the Correct Answer is Right**
Omphalitis, or navel infection, is a potential complication of umbilical cord separation, but it is not directly related to the metabolic effects of maternal diabetes on the fetus. The correct answer, Omphalitis, is an infection that can occur in any newborn, regardless of maternal diabetes status.

**Why Each Wrong Option is Incorrect**
**Option A:** Hypoglycemia is a common complication in neonates born to diabetic mothers due to the excess glucose crossing the placenta and causing the fetal pancreas to produce excess insulin, leading to hypoglycemia after birth.
**Option B:** Polycythemia, or an increased red blood cell count, can occur in neonates born to diabetic mothers due to the increased glucose levels stimulating erythropoiesis (red blood cell production) in the fetus.
**Option C:** Hypocalcemia, or low calcium levels, can occur in neonates born to diabetic mothers due to the increased glucose levels affecting calcium metabolism and bone mineralization in the fetus.

**Clinical Pearl / High-Yield Fact**
Neonates born to diabetic mothers are at increased risk of hypoglycemia, polycythemia, and hypocalcemia due to the excess glucose crossing the placenta and affecting fetal metabolism. It is essential to monitor these neonates closely for these complications and provide appropriate treatment to prevent long-term sequelae.

**✓ Correct Answer: D. Omphalitis. Omphalitis is a potential complication of umbilical cord separation but is not directly related to the metabolic effects of maternal diabetes on the fetus.**