## Core Concept
The Maternal Mortality Ratio (MMR) is a critical indicator used in public health and epidemiology to assess the risk of maternal death during pregnancy and childbirth. It is a measure that reflects the quality of healthcare in a given area. MMR is specifically expressed as the number of maternal deaths per 100,000 live births.

## Why the Correct Answer is Right
The MMR is calculated by dividing the number of maternal deaths during a given time period by the number of live births during the same period, then multiplying by 100,000. This results in a rate that quantifies the risk of maternal death relative to the number of live births. Expressing MMR per 100,000 live births allows for a standardized comparison across different populations and over time.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because MMR is not expressed as a rate per 1,000 live births; that measurement is more commonly used for infant mortality rates.
- **Option B:** This option is incorrect because MMR is specifically defined and used as a rate per 100,000 live births, not per 10,000 live births.
- **Option D:** This option is incorrect because expressing MMR as a rate per 1,000,000 population does not accurately reflect the risk of maternal mortality in relation to live births.

## Clinical Pearl / High-Yield Fact
A key point to remember is that MMR is a significant indicator of a country's healthcare quality and is often used by international organizations and governments to track improvements in maternal health. A lower MMR indicates better healthcare for pregnant women.

## Correct Answer: C. 100,000 live births.