Chorioamnionitis caused by gram-negative bacteria as an etiologic factor in preterm birth

Abstract

The role and microbiological causes of infection and inflammation of the chorioamnion were studied in 85 patients with spontaneous preterm deliveries (< 37 weeks) and in 85 control patients with full term deliveries. Microorganisms were isolated from the freshly separated chorioamnion in 55% of preterm and 26% of term deliveries (p < 0.001). Isolation rates of gram-negative enteric bacteria were significantly higher in preterm deliveries than in term deliveries (p < 0.001), whereas differences in the isolation of other bacterial species were not significant. Histological chorioamnionitis was noted in 49% of preterm and 14% of term deliveries (p < 0.001), and was strongly associated with a positive chorioamniotic culture in both groups (p < 0.001). Histological chorioamnionitis was noted in 94%, 54%, and 4% of membranes with gram-negative rods, other microbial species and negative cultures, respectively (p < 0.001). Preterm deliveries were also associated with significantly higher rates of bacterial vaginosis (38% vs. 14%) and isolation of vaginal pathogens (85% vs. 65%). In the case of the majority (88%) of chorioamniotic isolates the same species was isolated in the vagina. The findings suggest that gram-negative enteric rods are important placental pathogens responsible for sub-clinical chorioamnionitis and possibly preterm birth. The findings support the concept that microorganisms ascending from the lower genital tract produce local inflammation, which may result in preterm labour and delivery.

Histologic Chorioamnionitis and Preterm Delivery

“…One explanation could be empirical; the more tissue locations sampled, the greater the likelihood of finding a locus with a high number of polymorphonuclear leukocytes/high-powered field. However, these results highlight the challenges of comparing HCA results across studies that include only extraplacental membranes (23,41,43,48), only disc (24,25,38,40,53), or both (26,34,36,46).…”

“…Other studies examining term placentas have reported HCA prevalences ranging from 4 percent to 79 percent (23,34,(36)(37)(38)(39)(40)(41)(42)(43)51). These findings underscore the need to compare inflammatory cells/patterns in preterm placentas with those in term placentas to arrive at meaningful relations between HCA and preterm delivery.…”

“…In studies comparing term and preterm placentas, odds ratios for HCA have ranged from 0.8 to 5.9 (23,34,(36)(37)(38)(39)(40)(41)(42)(43). This wide range may be due, in part, to differences in maternal characteristics, excluded subgroups (e.g., hypertensives, medically indicated deliveries), preterm category (e.g., early vs. all preterm), and HCA definition.…”

“…Most studies can be grouped into one of two categories: those that have used inflammatory cell thresholds (i.e., polymorphonuclear leukocytes/high-powered field) (24,38,(43)(44)(45)(46)(47)(48) and those that have incorporated a complex HCA grading and/or staging approach (49)(50)(51). Within the first category, HCA criteria have varied with respect to 1) the tissue components included, for example, placental disc, extraplacental membranes, and cord (33,42,47,52), disc only (24,25,38,40,53), or extraplacental membranes only (41,43,44,48); 2) threshold, for example, ''any inflammation'' (25,33,34,42,52,53), greater than five polymorphonuclear leukocytes/ high-powered field (24,38,47), and greater than 10 polymorphonuclear leukocytes/high-powered field (43,45,46,48); and 3) number of high-powered fields that must exceed the threshold (43,46,48). In the second category, the detailed systems of staging/grading have also varied.…”

Management of Abnormal Vaginal Flora as a Risk Factor for Preterm Birth

“…Therefore, if PCR is used, frequent infection with E coli could be detected amongst these cases even when cultures were negative (Daoud et al, 2008). Also GBS and gram negative rods (Sherman et al, 1997) are frequent causes of intrauterine infections and histologic chorioamnionitis, often leading to midtrimester abortion, and even recurrences in two thirds of the women who have experienced it before.…”