**Core Concept**
Turner syndrome is a genetic disorder that affects females, characterized by the partial or complete absence of one X chromosome. Cardiovascular anomalies are common in Turner syndrome, and the most prevalent cardiac defect is a bicuspid aortic valve (BAV). This is due to the abnormal development of the aortic valve, which normally has three cusps, but in Turner syndrome, it often has only two cusps.

**Why the Correct Answer is Right**
The bicuspid aortic valve is a congenital anomaly where the aortic valve has only two cusps instead of the normal three. This can lead to aortic stenosis or insufficiency, which may cause symptoms such as chest pain, shortness of breath, or fainting. The pathophysiology of BAV involves the abnormal development of the aortic valve leaflets, which can lead to turbulent blood flow and valve dysfunction.

**Why Each Wrong Option is Incorrect**
* **Option A:** Coarctation of the aorta is a narrowing of the aortic isthmus, which is a different type of cardiovascular anomaly.
* **Option B:** Ventricular septal defect (VSD) is a hole in the septum between the two ventricles, which is not the most common cardiac anomaly in Turner syndrome.
* **Option C:** Atrial septal defect (ASD) is a hole in the septum between the two atria, which is not the most common cardiac anomaly in Turner syndrome.

**Clinical Pearl / High-Yield Fact**
Turner syndrome patients with BAV are at increased risk of aortic dissection or rupture, particularly if the valve is severely stenotic or regurgitant.

**Correct Answer: A. Bicuspid aortic valve**