**Core Concept**
The maternal mortality rate (MMR) is a crucial indicator of the quality of healthcare services for pregnant women. It measures the number of deaths due to pregnancy-related complications per a specific number of live births, providing insights into the effectiveness of maternal healthcare systems.

**Why the Correct Answer is Right**
The correct answer, 1,00,000 live births, is based on the World Health Organization's (WHO) standard definition of MMR. This ratio helps to standardize the measurement of maternal mortality across different countries and populations. The use of 1,00,000 live births as the denominator allows for a more meaningful comparison of maternal mortality rates between regions with varying population sizes. This definition is also consistent with the global health community's efforts to track and reduce maternal mortality.

**Why Each Wrong Option is Incorrect**
**Option A:** 1000 live births is too low a denominator, making the MMR artificially high and not representative of actual maternal mortality rates.
**Option C:** 10,000 live births is still too low, and using this denominator would result in a less accurate representation of maternal mortality.
**Option D:** 100 live births is an extremely low denominator, which would lead to an excessively high MMR and an inaccurate representation of maternal mortality.

**Clinical Pearl / High-Yield Fact**
The MMR is a key indicator of a country's or region's progress towards achieving the United Nations' Sustainable Development Goal 3 (SDG 3), which aims to end preventable maternal and child deaths by 2030.

**✓ Correct Answer: B. 1,00,000 live births**