The cervical mucus plug inhibits, but does not block, the passage of ascending bacteria from the vagina during pregnancy.

Objective To evaluate the microbial load and the inflammatory response in the distal and proximal parts of the cervical mucus plug. Design Experimental research. Population Twenty women with a normal, singleton pregnancy. Sample Vaginal swabs and specimens from the distal and proximal parts of the cervical mucus plug. Methods Immunohistochemistry, enzyme-linked immunosorbent assay, quantitative polymerase chain reaction and histology. Results The total bacterial load (16S rDNA) was significantly lower in the cervical mucus plug compared with the vagina ( p = 0.001). Among women harboring Ureaplasma parvum, the median genome equivalents/g were 1574 (interquartile range 2526) in the proximal part, 657 (interquartile range 1620) in the distal part and 60 240 (interquartile range 96 386) in the vagina. Histological examinations and quantitative polymerase chain reaction revealed considerable amounts of lactobacilli and inflammatory cells in both parts of the cervical mucus plug. The matrix metalloproteinase-8 concentration was decreased in the proximal part of the plug compared with the distal part ( p = 0.08). Conclusion The cervical mucus plug inhibits, but does not block, the passage of Ureaplasma parvum during its ascending route from the vagina through the cervical canal. [ABSTRACT FROM AUTHOR]