What causes chorioamnionitis?

Updated: May 08, 2018
  • Author: Fayez M Bany-Mohammed, MD; Chief Editor: Ted Rosenkrantz, MD  more...
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Maternal chorioamnionitis occurs when protective mechanisms of the urogenital tract and/or uterus fail during pregnancy or when increased numbers of microbial flora or highly pathogenic microorganisms are introduced into the urogenital environment. [45, 46, 47, 48]

Ascending infection into the vagina, then the cervix, and finally into the uterine cavity, fetal membranes, and placenta is the consequence of many factors (ie, innate host defenses, disrupted healthy bacterial flora, pathologic bacterial load, bacterial virulence factors, and toxin production). A short cervix has been recognized as either a risk factor or a surrogate for microbial invasion of the amniotic fluid. [11, 42, 49]

Urogenital hygiene is obviously important in establishing healthy bacterial flora. Healthy bacteria (ie, lactobacilli) [50]  and natural peptide antibiotics in the vagina and cervix may have roles in preventing infections during pregnancy. [51]  Mucus, phagocytes, and natural antibiotic proteins (ie, lactoferrin, lysozyme, beta defensins) in the cervicovaginal secretions attempt to maintain a normal bacterial flora. [46]  Bacterial interference, mainly produced via lactobacilli living in an acidic vaginal environment and producing bacteriocins, may help to keep pathogenic bacteria from gaining a foothold in the cervicovaginal secretions. [52] These mechanisms of host protection may be altered in a significant number of pregnant women who develop chorioamnionitis. The use of oral probiotics to alter vaginal flora and potentially reduce morbidities associated with intraamniotic infection has been studied extensively, but no clear cut benefits were realized. [53]

Oral hygiene may influence rectal and urogenital bacterial flora during pregnancy. Although the theory is controversial, intense interest has focused on a connection among periodontitis, abnormal rectal colonization, and preterm delivery, [54, 55] as well as whether treatment for periodontal disease during pregnancy decrease the incidence of preterm birth. [56] Orogenital contact may also alter either colonic or urogenital microbial flora and ultimately cause ascending infection and chorioamnionitis, as seen in some case reports. [57, 58]  

Currently, researchers are trying to understand how host defense mechanisms prevent urogenital infection during pregnancy. An intense area of research is the concept of bacterial communities living in the cervicovaginal area (microbiome) that are metabolically active to produce biochemicals (metalobome) that support their existence as well as prevent pathogenic bacteria from gaining access to the amniotic cavity and subsequently cause chorioamnionitis. [59, 60, 61] The prevalence and diversity of bacterial species in fetal membranes during preterm labor emphasizes that further research on this topic is needed. [62, 63] Metagenomics uses nonculture, molecular methods to delineate all microbes inhabiting an environment. Thus, the cervicovaginal and intestinal microbiome are under intense scrutiny to understand preterm labor, preterm premature rupture of membranes (PPROM), and chorioamnionitis relative to the mother, and necrotizing enterocolitis, sepsis, and neurologic injury relative to the newborn. Several published reports exist regarding using molecular methods to understand intrauterine infection, fetal inflammation, and preterm delivery. [61, 62, 64]

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