Cord blood hematopoietic progenitors undergo circadian and seasonal variations. The lowest values are obtained between 4:00 and 12:00, as well as between May and August. This represents the first observation of such rhythms before birth.
Baudoux, E., Beguin, Y., Cornu, G., Brichard, B., De Bruyn, C., De Bruyère, M., De Hemptinne, D., Delforge, A., Deneys, V., Fillet, G., Germeau, N., Joris, I., Lefèvre, P., Massy, M., Paulus, J. M., Raymakers, N., Schaaps, J. P., Sondag, D., Van Cauwenberge, J. R., et al. (1998). Circadian and seasonal variations of hematopoiesis in cord blood. Bone Marrow Transplantation, 22 Suppl 1, S12. https://hdl.handle.net/2078.5/55443 (Original work published 1998)