Normal reticulocyte count at bih is
**Core Concept**
Reticulocyte count is a measure of the number of reticulocytes (immature red blood cells) in the peripheral blood, which provides an indication of the bone marrow's production of red blood cells. In newborns, the reticulocyte count is typically higher than in adults due to the transition from fetal to adult hemoglobin production.
**Why the Correct Answer is Right**
At birth, the reticulocyte count is high due to the sudden increase in erythropoiesis (red blood cell production) as the fetus adapts to the loss of the placenta, which previously provided oxygen and nutrients. This increase in erythropoiesis is mediated by the release of erythropoietin, a hormone produced by the liver in the fetus and the kidneys in adults. As the newborn adapts to the increased demand for oxygen, the reticulocyte count gradually decreases to adult levels.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not reflect the expected reticulocyte count at birth.
* **Option B:** This option is incorrect as it does not accurately describe the expected reticulocyte count in newborns.
* **Option C:** This option is incorrect as it does not provide a valid value for reticulocyte count at birth.
**Clinical Pearl / High-Yield Fact**
A normal reticulocyte count in newborns is typically around 10-20%, which gradually decreases to 0.5-1.5% in adults. This decrease is due to the maturation of red blood cells and the regulation of erythropoiesis by erythropoietin.
**Correct Answer: C. 2-3%**