**Core Concept**
Transient tachypnea of the newborn (TTN) is a benign condition characterized by rapid breathing in the first 24 hours of life. It is caused by the delayed clearance of fetal lung fluid due to immature lung function and incomplete lung expansion after birth.

**Why the Correct Answer is Right**
The most common situation associated with TTN is delivery by cesarean section. This is because babies born via cesarean section have less opportunity to experience the normal birth process, which includes the initial gasping and crying that helps to clear fetal lung fluid. As a result, babies born via cesarean section may experience a delay in the clearance of this fluid, leading to TTN.

In addition, the pressure exerted by the uterus on the lungs during a cesarean section can also contribute to the delayed clearance of fetal lung fluid. This can lead to an accumulation of fluid in the lungs, causing respiratory distress and tachypnea.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not a common situation associated with TTN. While prematurity can contribute to respiratory problems in newborns, it is not the most common situation associated with TTN.
**Option B:** This option is not directly related to TTN. While maternal diabetes can increase the risk of respiratory distress in newborns, it is not the most common situation associated with TTN.
**Option C:** This option is not a common situation associated with TTN. While congenital heart disease can cause respiratory problems in newborns, it is not the most common situation associated with TTN.

**Clinical Pearl / High-Yield Fact**
A key factor in the diagnosis of TTN is the absence of other underlying conditions that could cause respiratory distress. If a baby is born via cesarean section and experiences tachypnea, but has no other underlying conditions, it is likely to be a case of TTN.

**Correct Answer: C.