Changes in the vaginal and rectal carriage of group B streptococci during pregnancy.

The group B streptococcus carrier status of pregnant women appears to be relatively unstable. By using multiple low vaginal and rectal samples cultured on 2 or more media, an overall carrier rate of 38% was found in 187 women. Sequential samples commonly showed changes in the nature of the carrier status with time. More carriers were detected late in pregnancy; women giving negative results early in pregnancy often produced positive cultures later and there was a significant tendency towards rectal positivity.