Human milk samples were collected from mothers delivering at term, preterm, and very preterm. Milk from the mothers was collected at 3 different time points after delivery corresponding to colostrum, transitional and mature milk and then concentrations of a range of immune factors and growth factors measured. Term and preterm colostrum were found to have very high levels of immune and growth factors, with some levels being higher in the preterm colostrum. However, the very preterm colostrum had lower levels of some factors than in term milk. The authors conclude that maternal lactogenic compensatory mechanisms may take effect only after 30 weeks gestation.

Cristina Castellote, Rosario Casillas, Carolina Ramirez-Santana, Francisco J. Perez-Cano, Margarida Castell, M. Gloria Moretones, M. Carmen Lopez-Sabater, and Angels Franch. Premature delivery influences the immunological composition of colostrum and transitional and mature human milk. J Nutr. 2011 Jun; 141(6):1181-7. Epub 2011 Apr 20.