Sequential C3 and C4 levels in human milk in relation to prematurity and parity.

Similarly to many immune molecules of human milk, C3 and C4 levels decrease during lactation. We investigated the influence, over the first three weeks of lactation, of both prematurity and parity on the sequential evolution of these levels. Milk C3 and C4 concentrations were measured by immunonephelometry in 494 individual samples collected from 76 lactating mothers. C3 and C4 concentrations were higher in milk from preterm or primiparous mothers. The major differences were observed in milk from days 5-8 and 9-20, likely due to pronounced interindividual variations in levels of days 1-4 milk. Milk from mothers of precocious (33 weeks' gestation or less) preterm newborns presented higher concentrations and a slower decrease of C3 and C4 levels than that from mothers of late (33-37 weeks' gestation) preterm newborns, when compared to term mothers. Finally, the inversion of the C3/C4 ratio occurring over time, previously reported, appeared later in milk from mothers of preterm newborns. The influence of prematurity was even greater in primiparous than in multiparous mothers. Both C3 and C4 levels therefore appear to be influenced in human milk by the parity and prematurity of the delivery. Mothers from preterm newborns seem to provide higher levels of C3 for a longer period post delivery.