**Core Concept**
Neonatal mortality rate (NMR) is a key indicator of the quality of healthcare for newborns. It is defined as the number of deaths of infants in the first 28 days of life per 1,000 live births in a given year.

**Why the Correct Answer is Right**
The correct formula for calculating NMR involves the number of deaths of infants within the first 28 days of life, divided by the total number of live births. This ratio is then multiplied by 1,000 to express the rate per 1,000 live births. The correct formula is: NMR = (Number of deaths in first 28 days / Total number of live births) x 1,000.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify the time frame for the deaths, which is crucial for calculating NMR.
* **Option B:** This option is incorrect because it refers to the infant mortality rate (IMR), which includes deaths of infants up to one year of age, not just the first 28 days.
* **Option C:** This option is incorrect because it mentions a different time frame and does not specify the denominator as live births.

**Clinical Pearl / High-Yield Fact**
To remember the formula for NMR, use the mnemonic "28 Days of Life" to associate the correct time frame with the calculation.

**Correct Answer: C. (Number of deaths in first 28 days / Total number of live births) x 1,000.**