**Core Concept**
The most common cause of abdominal swelling in newborns is often related to **congenital anomalies** or **developmental issues**. Abdominal swelling can be due to various reasons, including **gastrointestinal**, **genitourinary**, or **hepatic** causes.

**Why the Correct Answer is Right**
Since the correct answer is not provided, let's consider a common cause: **congenital intestinal obstruction**. This condition can lead to abdominal swelling due to the accumulation of intestinal contents, fluid, and gas. The **ileum** and **jejunum** are common sites for such obstructions.

**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific answer choice, it's challenging to provide a direct explanation. However, if it were an option like "infection," it would be incorrect because, although infections can cause abdominal swelling, they are not the most common cause in newborns.
**Option B:** Similarly, without the specific text, if we consider "trauma" as an example, it would be incorrect because trauma is not a common cause of abdominal swelling in newborns, given their protected environment.
**Option C:** If this option were "tumor," it would be incorrect because, although tumors can cause abdominal swelling, they are rare in newborns.
**Option D:** Without the text, if we assume "nephrotic syndrome," it would be incorrect because, while it can cause swelling, it's not typically the most common cause of abdominal swelling in newborns.

**Clinical Pearl / High-Yield Fact**
Newborns with abdominal swelling require immediate attention, as it can be a sign of a life-threatening condition. **Congenital diaphragmatic hernia** and **omphalocele** are critical diagnoses to consider.

**Correct Answer:** D. Congenital intestinal obstruction