**Core Concept**
Perinatal mortality is a measure of the number of fetal deaths (stillbirths) and early neonatal deaths (deaths within the first week of life) per 1,000 births. The denominator in perinatal mortality rate calculations includes all births, which is a critical aspect of understanding this metric.

**Why the Correct Answer is Right**
The correct denominator for perinatal mortality includes all births, which is a comprehensive approach to assess the overall health outcomes of a population. This is in contrast to other metrics that may focus on specific subsets of births. The denominator is crucial as it provides a baseline against which to compare the number of fetal and early neonatal deaths. This allows for a more accurate assessment of the risk factors and contributing factors to perinatal mortality.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incomplete and does not provide a clear denominator for perinatal mortality rate calculations.
**Option B:** This option may be a subset of births, but it is not a comprehensive denominator for perinatal mortality rate calculations.
**Option C:** This option is also a subset of births and does not account for the entire population of births.

**Clinical Pearl / High-Yield Fact**
When calculating perinatal mortality rates, it's essential to use the total number of births as the denominator to ensure an accurate representation of the population's health outcomes.

**Correct Answer:** C. All births.