Seasonal Variation of Chronic Villitis of Unknown Etiology

Introduction: Chronic villitis of unknown etiology (VUE) is a chronic inflammatory lesion of the placenta. VUE is hypothesized to result from an alloimmune response or as response to an unidentified infection. Lack of a seasonal trend is thought to support VUE as an alloimmune response, though data on seasonal VUE trends are limited. Methods: Data were obtained from a hospital in Chicago, Illinois, from 2011–2016. Placentas sent to pathology were reviewed using a standardized protocol, and VUE cases were identified based on an automated text search of pathology records. We used monthly VUE prevalence estimates to investigate the annual trend, and we used Poisson regression to evaluate seasonal variation in the number of VUE cases. Results: There were 79 825 deliveries within the study period. Pathologists evaluated 12 074 placentas and identified 2873 cases of VUE. Regression results indicate that the risk of VUE is 16% to 17% higher in the fall and winter as compared to the summer (fall relative risk [RR]: 1.17, 95% confidence interval [CI]: 1.06–1.29; winter RR: 1.16, 95% CI: 1.05–1.29). Discussion: Our results suggest that there may be seasonal variation in VUE prevalence, particularly for low-grade VUE. Future studies should evaluate seasonal variation in a representative sample rather than relying on pathology reports to estimate prevalence.