Thrombopoietic activity in newborn infants.

Platelet count and thrombopoietic activity were investigated in newborns and in infants during their first 4 months of life. Four-day-old newborns, although not thrombocytopenic, showed a significantly reduced platelet count as compared to that of control adults. Furthermore, a significantly lower thrombopoietic activity was found in the sera of newborns compared to that in the sera of adults. In addition, the thrombopoiesis-stimulating factor (TSF) activity in cord serum was significantly lower than that in the mothers' sera. Since 7 of 37 newborns examined in the present study showed a very low TSF activity, lower than that found in the saline controls, the possibility that an inhibitor for thrombopoiesis exists in the newborns is suggested and discussed. The follow-up study revealed a low TSF activity in the sera of 1-month-old infants followed by a gradually increased activity, reaching in the 4th month levels similar to those of adults. Concomitantly with the rise in TSF activity in the serum, an increased platelet count was observed.