Correlation between serum antibody-levels against group B streptococci and gestational age in newborns.

Sera from 33 newborn infants with gestational ages ranging from 27 to 41 weeks were tested by radioimmunoassay for IgG antibodies to surface antigens of group B streptococci (GBS) types Ia, Ib, II and III. Antibody levels to GBS antigens were positively correlated to gestational age and birthweight. However, only the correlations for anti-Ia and anti-II antibody levels reached statistical significance. Mean antibody concentrations in infants below 34 weeks of gestation were significantly lower for type Ia (P less than 0.001), type II (P less than 0.001) and type III (P = 0.05) than in infants above this limit. These findings might explain the higher rate of serious GBS-infections found among prematures as compared to full-term infants.