Preterm Birth: Associations With Genital and Possibly Oral Microflora

Abstract

Opportunistic pathogenic microbes are indigenous to the female lower genital tract and etiologic in many types of pelvic infections and, apparently, a portion of preterm birth (PTB) cases. Bacterial vaginosis (BV) is a clinical syndrome based on an altered genital microflora in which Gardnerella vaginalis; anaerobic species primarily among Prevotella, Porphyromonas, Bacteroides, Peptostreptococcus, and Mobiluncus; Mycoplasma hominis; and Ureaplasma urealyticum become predominant in vaginal secretions. This BV complex of microbes, compared to a normal vaginal microflora dominated by facultative lactobacilli, is associated with significantly increased risks for preterm labor, preterm premature rupture of membranes, PTB, and other perinatal infectious complications. Pathogenetic mechanisms include an ascending route of infection and/or inflammatory process due to microbial products and maternal and/or fetal response(s) with production of prostaglandins and cytokines. In the presence of periodontal disease, oral opportunistic pathogens and/or their inflammatory products also may have a role in prematurity via a hematogenous route. Fusobacterium nucleatum, a common oral species, is the most frequently isolated species from amniotic fluid cultures among women with preterm labor and intact membranes. Also, the species and subspecies of fusobacteria identified from amniotic fluid most closely match those reported from healthy and diseased subgingival sites, namely F. nucleatum subspecies vincentii and F. nucleatum subspecies nucleatum, compared to strains identified from the lower genital tract. Although these fusobacteria also could be acquired through cunnilingus from a partner, new data associating maternal periodontal disease with preterm low birth weight taken with the isolation of F. nucleatum, Capnocytophaga, and other oral species from amniotic fluid support further study of a possible additional route, oral-hematogenous, to PTB.

A prospective study to investigate the relationship between periodontal disease and adverse pregnancy outcome

“…However, this study failed to find such an association between pregnancy outcome and reported urinary tract infection, perhaps due to problems in diagnosing maternal genito-urinary tract infection, which can often be subclinical. 21 Other medication taken in early pregnancy was also associated with poor outcome: it may be regarded as a surrogate marker for medical problems which may themselves affect pregnancy outcome.…”

Identification and Characterization of a Novel Adhesin Unique to Oral Fusobacteria

“…During periodontal infection, its cell mass increases as much as 10,000-fold, making it one of the most abundant anaerobic species in the diseased sites (48). F. nucleatum is also one of the predominant anaerobes associated with preterm birth, having been frequently isolated from amniotic fluids and placentas of women delivering prematurely (27). F. nucleatum may originate in the oral cavity and be transmitted to the uterus via a hemotogenous route.…”

Endotoxin-Neutralizing Antimicrobial Proteins of the Human Placenta

“…This is undoubtedly due to the presence of highly effective fetal defense mechanisms that serve to limit the bacterial infection of placental tissues. The placenta is a highly selective mechanical and immunological barrier against the dissemination of infectious agents by hematogenous routes or by the ascending route from the vagina (18). These defenses serve to limit both the degree and frequency of bacterial colonization within the placenta.…”