**Core Concept**
At 36 weeks of gestation, a premature baby girl presents with polyhydramnios, bile-stained gastric aspirate, and a "double bubble sign" on radiography. This clinical picture suggests a condition affecting the gastrointestinal tract, specifically involving obstruction or malformation.

**Why the Correct Answer is Right**
The "double bubble sign" is a radiographic finding characteristic of duodenal atresia, a congenital obstruction of the duodenum. In this condition, the duodenum is either completely or partially blocked, preventing normal passage of intestinal contents. The resulting polyhydramnios can be attributed to the fetus's inability to swallow and absorb amniotic fluid. The bile-stained gastric aspirate and absence of meconium passage further support the diagnosis, as the obstruction prevents the normal passage of intestinal contents.

**Why Each Wrong Option is Incorrect**
**Option A:** This option might be tempting due to the presence of polyhydramnios, but esophageal atresia typically presents with difficulty feeding and regurgitation of feeds, which was not mentioned in the scenario.

**Option B:** Although pyloric stenosis can cause polyhydramnios and vomiting, it is more common in term infants and typically presents with projectile vomiting after feeding.

**Option C:** Intestinal obstruction at other levels (e.g., small bowel obstruction) might cause vomiting and abdominal distension, but the "double bubble sign" is more specific to duodenal atresia.

**Clinical Pearl / High-Yield Fact**
The "double bubble sign" is a classic radiographic finding in duodenal atresia, characterized by two air-filled structures (the stomach and the duodenum proximal to the obstruction) with no air in the small bowel or colon.

**Correct Answer:** C. Duodenal atresia.