At birth, an infant’s pulse may range from 120 to 160 beats per minute and may go as high as 180 upon excitation.
After birth, oxygen use increases, which stimulates an increase in the rate of red blood cell and hemoglobin production.
The white blood cell count at birth is very high—sometimes as much as 45,000 cells per microliter—but the count decreases rapidly by the seventh day. Recall that the white blood cell count of an adult is 5000–10,000 cells per microliter.