Abstract
BackgroundThe link between histologic acute chorioamnionitis and infection is well established in preterm deliveries, but less well-studied in term pregnancies, where infection is much less common.Methodology/Principal FindingsWe conducted a secondary analysis among 195 low-risk women with term pregnancies enrolled in a randomized trial. Histologic and microbiologic evaluation of placentas included anaerobic and aerobic cultures (including mycoplasma/ureaplasma species) as well as PCR. Infection was defined as ≥1,000 cfu of a single known pathogen or a ≥2 log difference in counts for a known pathogen versus other organisms in a mixed culture. Placental membranes were scored and categorized as: no chorioamnionitis, Grade 1 (subchorionitis and patchy acute chorioamnionitis), or Grade 2 (severe, confluent chorioamnionitis). Grade 1 or grade 2 histologic chorioamnionitis was present in 34% of placentas (67/195), but infection was present in only 4% (8/195). Histologic chorioamnionitis was strongly associated with intrapartum fever >38°C [69% (25/36) fever, 26% (42/159) afebrile, P<.0001]. Fever occurred in 18% (n = 36) of women. Most febrile women [92% (33/36)] had received epidural for pain relief, though the association with fever was present with and without epidural. The association remained significant in a logistic regression controlling for potential confounders (OR = 5.8, 95% CI = 2.2,15.0). Histologic chorioamnionitis was also associated with elevated serum levels of interleukin-8 (median = 1.3 pg/mL no histologic chorioamnionitis, 1.5 pg/mL Grade 1, 2.1 pg/mL Grade 2, P = 0.05) and interleukin-6 (median levels = 2.2 pg/mL no chorioamnionitis, 5.3 pg/mL Grade 1, 24.5 pg/mL Grade 2, P = 0.02) at admission for delivery as well as higher admission WBC counts (mean = 12,000cells/mm3 no chorioamnionitis, 13,400cells/mm3 Grade 1, 15,700cells/mm3 Grade 2, P = 0.0005).Conclusion/SignificanceOur results suggest histologic chorioamnionitis at term most often results from a noninfectious inflammatory process. It was strongly associated with fever, most of which was related to epidural used for pain relief. A more ‘activated’ maternal immune system at admission was also associated with histologic chorioamnionitis.
Highlights
It has long been believed that the histologic diagnosis of acute chorioamnionitis is inextricably linked with infection [1,2,3]
The cases with infection grew a variety of organisms known to populate the cervical/vaginal environment including Ureaplasma, Group B Streptococcus (GBS), Staphylococcal species and Propionibacterium (Table 1)
We found that in low-risk, term gestations histologic acute chorioamnionitis is not associated with placental membrane infection, despite the robust microbiologic methods we used for detecting infection
Summary
It has long been believed that the histologic diagnosis of acute chorioamnionitis is inextricably linked with infection [1,2,3]. The connection has been well established when histologic chorioamnionitis is seen in preterm placentas with many studies demonstrating a high association with documented infections [4,5,6]. These studies have used a variety of techniques to document true infection including cultures of amniotic fluid just before the time of delivery [6]and direct culture of the placenta after delivery [4,7,8]. The etiology of culture negative histologic chorioamnionitis is unknown Many have suggested it results from inadequate or non-inclusive culturing practices, as some infectious agents are difficult to identify without careful and specific culture conditions (for example mycoplasmas and chlamydiae). The link between histologic acute chorioamnionitis and infection is well established in preterm deliveries, but less well-studied in term pregnancies, where infection is much less common
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