Objective To evaluate the transplacental transfer of anti-group B Streptococcus (GBS) antibodies and immunoglobulin G (IgG) in term and preterm newborns and compare the serum levels between these two groups.

Methods Transversal study, with 44 newborns infants (18 preterm and 26 term). Blood and umbilical cord samples were collected from the mothers and from their respective newborn. Total IgG measurements were performed using nephelometry; antibodies anti-GBS were evaluated by the ELISA test.

Results The mean serum levels of anti-GBS antibodies in mothers of preterms were 1570.72 (in titles), ranging from 588 to 3829; in terms’ mothers the mean level was 1786.08, ranging from 456 to 5200. In both groups of mothers the levels were similar. Anti-GBS antibody levels in the preterm were significantly lower compared with term newborns. The mean serum level of anti-GBS antibodies in preterms was 1059.22, ranging from 416 to 3924, whereas in term newborns the mean level was 2025.50, ranging from 542 to 5476.

Conclusions Transplacental transfer of IgG and anti-GBS antibodies have been demonstred in term and preterm newborns. The transfer of IgG and antibodies was less effective in preterms whose levels were significantly lower compared with the levels of their mothers and term newborns. The positive correlation between the levels of IgG and anti-GBS antibodies with gestational age proves the importance of prematurity as a determining factor in the low serum concentrations in the components of the newborn’s immunological repertoire. Mothers of term and preterm newborns had no difference between the levels of anti-GBS antibodies.