A 26-year-old woman at 29 weeks gestation experienced epigastric pain after a large meal. What is the most likely diagnosis for this symptom?

Epigastric pain following a large meal during the third trimester of pregnancy is often associated with gastrointestinal changes that occur due to both physiological and mechanical factors. The correct diagnosis in this scenario is cholelithiasis, which refers to the presence of gallstones.

During pregnancy, hormonal changes lead to decreased bile salt secretion and an increased cholesterol level in bile, making the formation of gallstones more likely. Additionally, the enlarging uterus can exert pressure on the gallbladder and the surrounding organs, which may exacerbate symptoms. When a large meal is consumed, particularly one that is high in fat, it can lead to increased gallbladder contraction and potentially trigger pain if gallstones are present.

While indigestion may seem plausible, especially after a large meal, the specific mention of epigastric pain aligns more closely with complications related to the gallbladder. In contrast, influenza and urinary tract infections typically present with systemic symptoms like fever or dysuria rather than isolated epigastric pain. Thus, considering the context and symptoms, cholelithiasis is the most likely diagnosis for the woman's epigastric pain after eating.