**Core Concept**
The question is testing the student's knowledge of the leading cause of maternal mortality, a critical aspect of obstetrics and gynecology. Maternal mortality refers to the death of a woman during pregnancy, childbirth, or within 42 days of termination of pregnancy, from any cause related to or aggravated by the pregnancy or its management.

**Why the Correct Answer is Right**
The single most common cause of maternal mortality is **hemorrhage**. Hemorrhage accounts for approximately 27% of all maternal deaths worldwide. This is often due to excessive bleeding during or after delivery, which can be caused by placental abruption, uterine atony, or other conditions. The mechanism involves the failure of the uterus to contract effectively after delivery, leading to severe bleeding that cannot be controlled.

**Why Each Wrong Option is Incorrect**
* **Option A:** **Hypertension** is a significant cause of maternal mortality, but it is not the leading cause. Hypertension-related complications, such as eclampsia and stroke, can be life-threatening, but they are not as common as hemorrhage.
* **Option B:** **Infections** are another major cause of maternal mortality, particularly in low-resource settings. However, they are not the leading cause globally. Infections can lead to severe sepsis, organ failure, and death, but they are not as prevalent as hemorrhage.
* **Option C:** **Cardiovascular disease** is a significant cause of maternal mortality, particularly in developed countries. However, it is not the leading cause globally. Cardiovascular disease can lead to heart attacks, strokes, and other life-threatening complications, but it is not as common as hemorrhage.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the leading causes of maternal mortality vary by region and country. However, hemorrhage is consistently the leading cause globally, emphasizing the need for effective management of postpartum bleeding and prompt access to emergency obstetric care.

**Correct Answer:** C. Cardiovascular disease