Relation between maternal age and serum concentration of IgG antibody to type III group B streptococci

Coded serum samples collected from healthy obstetric patients at delivery were examined by ELISA for IgG antibody to the purified type III polysaccharide of group B streptococci. When 217 patients were divided into 4 groups according to age (group I =16-20 years, n = 56; group II = 21-25, n = 53; group III = 26-30, n = 54; group IV = 31-35, n = 54), antibody concentrations were significantly lower in group I than in older patients. Fewer subjects in group I had measurable antibody levels (> or = 0.05 microgram/mL) than in groups II-IV (41% vs. 76%, P < .001). The geometric mean in group I (0.09 microgram/mL) was significantly lower (P < .001) than in the older groups (0.23, 0.19, and 0.20 microgram/mL, respectively) with little or no overlap of the 95% confidence limits (1.96 SE) about the means. These findings may be relevant to the observation of a significantly greater risk of both early- and late-onset group B streptococcal disease in infants of teenage mothers.