**Core Concept**
The infant mortality rate is a key indicator of a country's overall health and well-being, reflecting the quality of prenatal, delivery, and postnatal care. It is calculated as the number of deaths of infants under one year of age per 1000 live births. The denominator represents the total number of live births in a given population.

**Why the Correct Answer is Right**
The correct answer is based on the World Health Organization's (WHO) standard definition of infant mortality rate. The numerator is the number of infant deaths, while the denominator is the number of live births. The ratio of infant deaths to live births is then expressed per 1000 live births, making it easier to compare and track trends across different populations. This standardization helps to ensure that the infant mortality rate is a meaningful and comparable indicator of health outcomes.

**Why Each Wrong Option is Incorrect**
* **Option A:** Using per live birth as the denominator would result in an extremely high rate, making it difficult to interpret and compare across different populations.
* **Option B:** Expressing the infant mortality rate per 100 live births would be an oversimplification and would not provide a clear picture of the health outcomes in a given population.

**Clinical Pearl / High-Yield Fact**
When analyzing infant mortality rates, it's essential to consider the numerator (number of infant deaths) and the denominator (number of live births) separately, as changes in either can affect the overall rate. Additionally, infant mortality rates can be influenced by various factors, including prenatal care, birth weight, and access to healthcare services.

**✓ Correct Answer: C. Per 1000 live births**