RBC values in low-birth-weight infants during the first seven weeks of life.

Hemoglobin, RBC mean corpuscular volume (MCV), and other RBC indices were studied in a group of 40 infants, each with a birth weight of less than 1,500 g. Results indicated that the hemoglobin level fell from 18.2 +/- 2.7 g/dL at birth to a low of 9.5 +/- 1.5 g/dL at 6 weeks of age. During this time, the MCV declined from 115 +/- fentoliters (fL) to 97 +/- 5 fL and did not again rise as the hemoglobin stabilized. Although the decline in MCV may simply reflect an aging RBC population, these data raise the possibility that RBC size may in part be determined by postnatal factors independent of time from conception.