- The RBC count increases during the first 24 hours of life, remains at this plateau for about 2 weeks and then slowly declines.
- This “polycythemia of the newborn” may be explained by in utero hypoxia, which becomes more pronounced as the fetus grows. Hypoxia, the trigger for increased secretion of erythropoietin, stimulates erythropoiesis. At birth, the physiologic environment changes and the fetus makes the transition from its placenta-dependent oxygenation to the increased tissue oxygenation of the lungs. This increased oxygen tension suppresses erythropoietin production, which is followed by a decrease in RBC and hemoglobin production;21
-Normal development of human fetal hematopoiesis between eight and seventeen weeks gestation. Studies show that erythropoietin levels before birth are equal to or greater than adult levels with a gradual drop to near zero a few weeks after birth;22 this decline corresponds to the physiologic anemia seen at 5 to 8 weeks of life, with the RBCs reaching their lowest count at 7 weeks of age and hemoglobin reaching its lowest concentration at 9 weeks of age.
-The span of erythrocytes in full term infants is shorter than that of adult erythrocytes; the life span of RBCs in premature infants is considerably shorter. The more immature the infant is the greater the degree of reduction.
- This “polycythemia of the newborn” may be explained by in utero hypoxia, which becomes more pronounced as the fetus grows. Hypoxia, the trigger for increased secretion of erythropoietin, stimulates erythropoiesis. At birth, the physiologic environment changes and the fetus makes the transition from its placenta-dependent oxygenation to the increased tissue oxygenation of the lungs. This increased oxygen tension suppresses erythropoietin production, which is followed by a decrease in RBC and hemoglobin production;21
-Normal development of human fetal hematopoiesis between eight and seventeen weeks gestation. Studies show that erythropoietin levels before birth are equal to or greater than adult levels with a gradual drop to near zero a few weeks after birth;22 this decline corresponds to the physiologic anemia seen at 5 to 8 weeks of life, with the RBCs reaching their lowest count at 7 weeks of age and hemoglobin reaching its lowest concentration at 9 weeks of age.
-The span of erythrocytes in full term infants is shorter than that of adult erythrocytes; the life span of RBCs in premature infants is considerably shorter. The more immature the infant is the greater the degree of reduction.
Erythrocytes morphology remains macrocytic from the first 11 weeks of gestation until day 5 of postnatal life.23
The erythrocytes of newborn infants are markedly macrocytic at birth, with a mean cell volume (MCV) in excess of 110 fl/cell. The MCV begins to fall after the first week, reaching adult values by the ninth week. The average MCV for full-term infants is 110±15 fL; however, a sharp decrease occurs during the first 24 hours of life. The MCV continues to decrease to 90±12 fL in 3 to 4 months. The more premature infant higher the MCV. A newborn with an MCV of less than 94 fL should be evaluated for α-thalassemia or iron deficiency.1,1
Esan AJ. Hematological differences in newborn and aging: a review study. Hematol Transfus Int J. 2016;3(3):178-190. DOI: 10.15406/htij.2016.03.00067
