## Core Concept
The Maternal Mortality Ratio (MMR) is a measure of maternal mortality in a given population, reflecting the risk of death from pregnancy-related complications. It is expressed as a ratio of maternal deaths to live births. The MMR is a critical indicator of the quality of healthcare in a region.

## Why the Correct Answer is Right
The denominator in the Maternal Mortality Ratio (MMR) calculation is indeed **live births**. The MMR is calculated as the number of maternal deaths per 100,000 live births. This means for every 100,000 live births, how many maternal deaths occur. The formula is: (Number of maternal deaths / Number of live births) x 100,000. Using live births as the denominator allows for the assessment of the risk of maternal death in relation to the number of pregnancies that resulted in live births.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not accurately represent the denominator used in the calculation of MMR.
- **Option B:** This option is incorrect because it suggests a different denominator, which is not used for MMR calculations.
- **Option D:** This option is incorrect because it proposes another alternative denominator, which does not accurately reflect the standard calculation for MMR.

## Clinical Pearl / High-Yield Fact
A key point to remember is that MMR is a significant health indicator that reflects the quality and accessibility of healthcare services, particularly prenatal, delivery, and postnatal care. A high MMR indicates a higher risk of maternal death and often points to inadequate healthcare infrastructure or services.

## Correct Answer: B. live births