Placental Pathogens Associated With Adverse Maternal and Neonatal Outcomes

Bacterial infection at the maternal-fetal interface contributes to adverse pregnancy outcomes, including preterm birth, chorioamnionitis, and sepsis. Despite evolving obstetric practices that may influence microbial patterns, recommended clinical algorithms for prophylaxis and treatment rely on outdated data. Furthermore, the pathogenic organisms associated with adverse outcomes remain incompletely characterized.

We conducted a retrospective study of placental cultures from a high-risk obstetric cohort from a single hospital system between 2014 and 2019 (n = 714). Placental cultures were obtained from deliveries at high risk for infection: (eg, preterm birth or suspected chorioamnionitis). Placental cultures were stratified into pathogenic and nonpathogenic. Associated clinical outcomes, histopathology, and antimicrobial susceptibility patterns were compared.

Pathogenic organisms were identified in 69% of cultures (492 of 714). Group B Streptococcus (n = 161; 22.5% of total isolates) and Escherichia coli (n = 53; 7.4% of total isolates) were the most common pathogens isolated; we also identified additional pathogens, including Enterococcus faecalis (n = 44), Haemophilus (n = 37), Prevotella (n = 32), and Bacteroides species (n = 23). Pathogenic cultures were correlated with significantly higher rates of composite adverse maternal (27.0% vs 17.6%; P = .006) and neonatal (78.9% vs 60.6%; P < .001) outcomes, as well as histopathologic chorioamnionitis (72.5% vs 60.9%; P = .003). Antimicrobial resistance for recommended empiric regimens ranged from 47.1% to 87.8%.

Bacterial pathogens isolated from the placenta in high-risk pregnancies are associated with perinatal morbidity. Group B Streptococcus and E coli remain common, and E faecalis, Haemophilus spp, and anaerobes such as Prevotella may represent emerging pathogens underrecognized in contemporary obstetric practice. Placental cultures may serve as a valuable surveillance tool for informing empiric antibiotic strategies in pregnancy.