**Core Concept**
The most common cause of infant mortality is a critical public health concern, primarily related to the vulnerability of newborns and infants to various infectious and non-infectious diseases. This concept involves understanding the epidemiology and risk factors associated with infant mortality.

**Why the Correct Answer is Right**
The leading cause of infant mortality worldwide is preterm birth complications, often resulting from premature rupture of membranes, chorioamnionitis, or placental abruption. Preterm infants are at increased risk of developing respiratory distress syndrome, intraventricular hemorrhage, and sepsis due to their immature lungs and immune systems. Additionally, preterm birth is associated with increased risk of long-term developmental and cognitive impairments.

**Why Each Wrong Option is Incorrect**
**Option A:** Congenital anomalies are a significant cause of infant mortality, but they are not the most common cause. Congenital anomalies account for around 2-3% of infant deaths globally.
**Option B:** Neonatal tetanus is a preventable cause of infant mortality in developing countries, but it is not the leading cause globally. The introduction of tetanus toxoid in maternal immunization programs has significantly reduced its incidence.
**Option C:** Asphyxia is a major cause of infant mortality, particularly in low- and middle-income countries. However, it is not the most common cause globally.

**Clinical Pearl / High-Yield Fact**
Preterm birth is a leading cause of infant mortality, emphasizing the importance of prenatal care, maternal health, and prevention of preterm labor.

**Correct Answer: C. Asphyxia**