Humoral regulation of erythropoiesis and thrombopoiesis in appropriate and small for gestational age infants.

Fourteen infants with birth weight appropriate for gestational age (AGA) and 16 small for gestational age (SGA) infants were investigated for haemoglobin concentration, haematocrit level and thrombocyte count on the first day of life. Cord serum was tested for erythropoietin (ESF) and thrombopoietin (TSF) activity. The same investigations were performed on venous blood and serum from 18 healthy adult individuals. SGA infants had higher haemoglobin concentration and haematocrit level (p less than 0.05), and lower platelet count (p less than 0.001) than AGA infants. Significant ESF activity was present in cord serum, but was not detectable in serum from adults. Significant TSF activity was present in cord serum as well as in serum from adults, with higher levels in the newborn infants (p less than 0.05). An inverse relationship was found between serum TSF activity and the number of platelets in adults, which was not demonstrable in newborn infants. Long-term intrauterine hypoxia because of placental dysfunction may be the reason for polycythemia and thrombocytopenia in SGA infants. Thrombocytopenia may be caused by competitive mechanisms on common stem cells for erythropoiesis and thrombopoiesis, shunting stem cells in direction of erythropoiesis during hypoxic exposure. Normal serum TSF activity in SGA infants indicates that lack of the humoral factor for platelet production is not the reason for the thrombocytopenia in these infants. A negative feed-back mechanism may exist between platelet number and TSF production.