## Core Concept
Maternal hyperglycemia, typically seen in gestational diabetes mellitus (GDM) or pre-existing diabetes mellitus, can lead to various complications in the fetus and newborn. These complications arise due to the teratogenic effects of hyperglycemia and the resultant fetal hyperinsulinism.

## Why the Correct Answer is Right
Fetal macrosomia (or **macrosomia**) is a well-recognized complication of maternal hyperglycemia. The high glucose levels cross the placenta, stimulating the fetal pancreas to secrete excess insulin, which in turn promotes growth and fat deposition, leading to macrosomia. **Polyhydramnios** can also occur due to fetal macrosomia causing increased fetal urine production. **Respiratory distress syndrome (RDS)**, however, is more commonly associated with prematurity and not directly with maternal hyperglycemia; in fact, infants of diabetic mothers are at higher risk for **delayed lung maturation** but can experience respiratory issues due to other factors. **Shoulder dystocia** is a complication related to fetal macrosomia.

## Why Each Wrong Option is Incorrect
- **Option A (Macrosomia):** This is indeed a complication of maternal hyperglycemia, as explained.
- **Option B (Polyhydramnios):** This condition, characterized by an excessive amount of amniotic fluid, can be associated with maternal hyperglycemia due to fetal macrosomia and increased urine production.
- **Option D (Shoulder dystocia):** This is a known complication of fetal macrosomia, which results from maternal hyperglycemia.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that maternal hyperglycemia can lead to **fetal macrosomia**, which increases the risk of **shoulder dystocia** during delivery. Early identification and management of gestational diabetes are crucial to prevent these complications.

## Correct Answer: C. Respiratory distress syndrome.