Haemoglobin concentrations and erythropoietin levels in appropriate and small for gestational age infants.

Capillary Hb concentration on the first day of life was registered in 201 infants with weight appropriate for gestational age (AGA) and in 99 infants small for gestational age (SGA). In both groups Hb increased towards term (P less than 0.01), while the SGA infants reached higher Hb concentration at term (21.5 +/- 1.9 g/dl; mean +/- SD) than the AGA infants (17.9 +/- 1.5 g/dl) (P less than 0.001). The cord serum erythropoietin (EP) level increased towards term equally in both groups. Delivery did not seem to influence the EP level as same values were obtained in cord serum from infants delivered by elective cesarean section as after uncomplicated vaginal delivery. No correlation was found between cord serum EP and first day capillary PCV. Postnatally a rapid fall in the EP level occurred. In healthy adults no serum EP activity was detected. It is suggested that increasing hypoxia, rapid growth, and shift from hepatic to myeloid erythropoiesis may be related to the increasing Hb concentration and serum EP level towards term. Improvement of oxygenation during air breathing may cause the decreasing serum EP level after birth.