Cord blood collection before and after placental delivery: levels of nucleated cells, haematopoietic progenitor cells, leukocyte subpopulations and macroscopic clots.

The number of nucleated cells infused into the recipient of a cord blood (CB) transplant has emerged as the most important factor affecting the probability and speed of engraftment. At present, there is no international consensus on the procedure of CB collection in the maternity ward. In order to maximise the yield of viable cells in a CB unit, we aimed to investigate the efficiency of CB collection, with respect to the time of delivery of the placenta. We analysed stem and progenitor cells in terms of CD34+ cell content and colony-forming activities, lymphocyte subpopulations and the presence of macroscopic clots in 93 paired CB samples, collected before and after the delivery of the placenta. Our results demonstrated that the median concentrations of nucleated cells and total colony-forming unit (CFU) were significantly lower in CB collected after placenta delivery by 9.5% (P < 0.001) and 11.6% (P = 0.015), respectively, when compared to their counterparts collected before placental delivery. A reduction of granulocytes (P < 0.001), monocytes (P < 0.001) and CD19+ B lymphocytes (P = 0.031) was observed, with no significant change in the proportion of T cell subsets (CD4+, CD8+ cells) or activated T cells (CD25+, CD45RO+ cells) in samples collected after placenta delivery. The incidence of macroscopic clots was also higher in these samples (31% vs 1%, P < 0.001). The reduction of stem and progenitor cells correlated significantly with that of major cell populations, indicating a general cell loss, possibly due to clotting activities developed with time. Our study has documented strong evidence for recommending the collection of CB before the delivery of the placenta.