## Core Concept
Perinatal mortality refers to the death of a fetus or newborn within a specific period around birth. It is a critical indicator of the quality of prenatal care, obstetric care, and neonatal care. The perinatal period is generally defined as the period from the 28th week of gestation to the 7th day of life.

## Why the Correct Answer is Right
The correct answer, **per 1000 births**, is the standard unit for expressing perinatal mortality. Perinatal mortality rate is calculated as the number of stillbirths and deaths in the first week of life per 1000 births (live births and stillbirths). This expression helps in understanding the risk of death in the perinatal period and facilitates comparison across different populations.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incomplete and does not provide a clear unit or expression for perinatal mortality.
- **Option B:** Similarly, this option lacks specificity and does not accurately represent the standard unit for expressing perinatal mortality.
- **Option D:** This option also does not accurately represent the standard expression for perinatal mortality.

## Clinical Pearl / High-Yield Fact
A key point to remember is that perinatal mortality rates are crucial for assessing the effectiveness of healthcare systems, especially in the areas of maternal and child health. A lower perinatal mortality rate indicates better healthcare services.

## Correct Answer: C. per 1000 births