**Core Concept**
Maternal and Child Health (MCH) services are essential components of healthcare systems worldwide, focusing on the well-being of mothers, newborns, and children. Quality indicators are crucial to evaluate the effectiveness and efficiency of these services, ensuring that they meet international standards and improve health outcomes.

**Why the Correct Answer is Right**
The quality indicator of MCH services is often measured by the **Maternal Mortality Ratio (MMR)**. MMR is the number of deaths among mothers due to complications related to pregnancy and childbirth per 100,000 live births. It reflects the quality of antenatal, delivery, and postnatal care provided to mothers. A lower MMR indicates better quality MCH services.

**Why Each Wrong Option is Incorrect**
**Option A:** Low Infant Mortality Rate (IMR) is a crucial indicator of child health, but it does not specifically measure the quality of MCH services.
**Option B:** Caesarean Section Rate may be an indicator of obstetric practices, but it is not a direct measure of MCH service quality.
**Option C:** Skilled Birth Attendance (SBA) rate is an essential component of MCH services, but it is not a quality indicator in itself.

**Clinical Pearl / High-Yield Fact**
Remember that the Maternal Mortality Ratio (MMR) is a composite indicator that reflects the quality of antenatal, delivery, and postnatal care provided to mothers. It is essential to track and reduce MMR to improve MCH services and save lives.

**Correct Answer: D. Maternal Mortality Ratio (MMR)**