**Core Concept**
In newborns, congenital malformations can be an indicator of maternal metabolic disorders, such as insulin-dependent diabetes mellitus (IDDM). The malformation associated with IDDM is a result of the teratogenic effects of hyperglycemia on fetal development.

**Why the Correct Answer is Right**
The malformation specific to maternal IDDM is **macrosomia**, which is characterized by excessive birth weight and length. This occurs due to the increased glucose availability in the maternal bloodstream, leading to excessive fetal growth. The excess glucose crosses the placenta and is used by the fetus for energy production, leading to increased insulin production and subsequent growth. This condition is often referred to as "fetal macrosomia" or "macrosomia neonatorum."

**Why Each Wrong Option is Incorrect**
* **Option A:** Intrauterine growth restriction (IUGR) is associated with maternal hypertension, chronic kidney disease, or other conditions that impair placental function, not IDDM.
* **Option B:** Congenital heart defects can be associated with various maternal conditions, including phenylketonuria, maternal hypothyroidism, or even maternal diabetes, but they are not specific to IDDM.
* **Option C:** Caudal regression syndrome is associated with maternal diabetes, but it is not specific to IDDM and can be seen in both type 1 and type 2 diabetes.

**Clinical Pearl / High-Yield Fact**
Fetal macrosomia can be an indicator of maternal IDDM, and it is essential to screen pregnant women with diabetes for this condition to prevent potential complications.

**Correct Answer: C. Macrosomia**