**Core Concept**
Macrosomia refers to a condition where a newborn baby is significantly larger than average. This condition is often associated with **gestational diabetes** and **genetic factors**. The birth weight of these infants usually exceeds 4000 grams or 4500 grams, depending on the criteria used.

**Why the Correct Answer is Right**
The correct answer is related to the definition of macrosomia, which involves an infant being born with a birth weight above the 90th percentile or more than 4000-4500 grams. This condition can lead to complications during delivery, such as **shoulder dystocia**, and may require **cesarean section**. The exact birth weight criterion may vary, but the essence of macrosomia is the unusually high birth weight.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because macrosomia is not defined by a low birth weight.
**Option B:** This option is incorrect as it does not specify the condition of macrosomia.
**Option C:** This option is also incorrect as it does not accurately describe macrosomia.
**Option D:** This option might seem plausible but is incorrect because it does not accurately represent the definition of macrosomia.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that macrosomia can be associated with **fetal insulin resistance** and **maternal diabetes**, highlighting the importance of managing blood glucose levels during pregnancy.

**Correct Answer:** D. Birth weight over 4000 grams or 90th percentile.