The correlation between placental histology and microbiologic infection in the diagnosis of chorioamnionitis in preterm delivery.

Introduction: This study sought to investigate the correlation between histologically proven chorioamnionitis and placental bacteriologic infection in preterm births.

Methods: Women who gave birth before 34 + 0 weeks' gestation at a tertiary medical center between the years 2018-2019 were identified by a database review. Data was collected on clinical characteristics and findings on placental histology, cultures, and polymerase chain reaction. The correlation between histologically confirmed chorioamnionitis and bacteriologic infection was evaluated.

Results: Of 183 placentas included in the study, 88 (48.1%) were histologically positive for chorioamnionitis and 95 (51.9%) were negative. Baseline characteristics were similar in the patients with and without chorioamnionitis. Concordance rates between the histology and microbiology results in the two groups were 51.1% and 64.2%, respectively. Similar types of bacterial microorganisms were isolated in both groups, though at different rates. On chi-square analysis of association, a positive microbiological study had a sensitivity of 51.1%, specificity of 64.2%, and positive predictive value of 56.9% for predicting histologically confirmed chorioamnionitis. Histologically confirmed chorioamnionitis was associated with higher antepartum white blood cell count (14.2 ± 4.6 vs 12.3 ± 3.3 K/μL; p = 0.01), higher rate of clinically suspected chorioamnionitis (10.2% vs 1.1%, p = 0.02), and higher rate of neonatal adverse composite outcome (36.4% vs. 22.1%, p = 0.009).

Discussion: The correlation between histologic and bacteriologic placental findings in the setting of early premature delivery is not high, nor is the clinical yield of placental bacteriology. The discordant results might be explained by early stage of bacterial infection, hard-to-cultivate bacterial species, noninfectious conditions, or contamination of the placental surfaces during passage through the vaginal tract.