In adults, red blood cells are broken down and replaced at pretty much the same rate. In a newborn however, this isn’t the case.
Newborns are not able to manufacture their own blood cells until they are about 6 to 8 weeks old.
Because the baby begins to lose red blood cells naturally after birth, this means every newborn has slight physiologic anemia beginning at about age 4 weeks. This is a normal physiological process, and usually does not require any treatment and does not cause concern. Babies outgrow this anemia at around 8 weeks of age.
There are several conditions which can cause accelerated loss of red blood cells in your newborn. For example, if your baby was premature, he was not born with his full blood volume, and he will have blood taken for laboratory testing.
The more premature your baby, the greater the likelihood that he will need a transfusion to overcome anemia. If you and premature baby have a different blood type, your baby will have more red blood cells break down after his birth.
However you feed your baby, either with breast milk which naturally contains iron, or with iron-fortified formula, your baby will receive optimal amounts of dietary iron.
When your baby begins to rely less on a liquid diet and becomes able to eat cereal, at around age 4 to 6 months, iron-fortified cereal is a good choice for continuing health.