Gram stain in the rapid determination of maternal colonization with group B beta-streptococcus.

To determine the usefulness of the Gram stain as a screening technique for maternal colonization with group B beta-streptococcus, we produced a Gram stain from a cervicovaginal swab taken at the time of sterile speculum examination in patients being evaluated for preterm rupture of membranes or preterm labor. The stain's interpretation was compared against the culture taken during the same examination. We found a sensitivity of 38% and a negative predictive power of 86%. Our findings differ from those of previous studies, and do not support the Gram stain as a useful screening approach for detection of colonization with this organism.