The effects of gestation on circulating progenitor cells

The frequency of BFU‐E in second‐trimester fetal blood (484 ± 104/105) falls progressively during gestation to a value of 69 ± 41/105 in cord bloods of 36 weeks gestation and beyond, but this is still significantly greater than adult blood values of 14 ± 8 (P < 0.01). BFU‐E obtained from unfractionated peripheral blood mononuclear cells from fetuses/neonates less than 36 weeks gestation were more sensitive to erythropoietin than adult BFU‐E, but the sensitibvity of highly purified BFU‐E obtained from secondtrimester fetal liver was similar to that in adult cells. Almost maximal growth of BFU‐E from purified fetal progenitor cells could be achieved with erythropoietin alone, whereas adult cells required the presence of other factors with ‘burstpromoting activity’.