Chronic villitis of unknown aetiology: an Australian institution's 5-year experience.

Villitis of unknown aetiology (VUE) is a chronic inflammatory condition of the placenta that is associated with increased morbidity and mortality in perinatal medicine. The cause remains elusive and recent studies have explored immune-mediated, infectious and environmental triggers in the pathogenesis of VUE. The objective of this study was to identify the characteristics of VUE diagnoses at Mater Mothers' Hospital over a 5-year period, including any association with seasons, maternal age and histological patterns of the disorder. We retrospectively reviewed reports for placentas sent to Mater Pathology, Brisbane, over 5 years (December 2015 to November 2020). Case level data were retrieved including maternal age, the month of delivery, gestational age, parity, VUE status, recurrence, histopathological subtype and grade. Univariable and multivariable logistic regression was used to estimate the unadjusted and adjusted association between VUE and season, maternal age and trimester at delivery. While more placentas were examined during summer than winter (p=0.005), there was no evidence of seasonal variation in the incidence of VUE over the 5 years (p=0.17). Both univariable and multivariable logistic regression analyses showed that VUE increased with maternal age (p<0.001) and gestational age (9.8% of examined placentas in the third trimester compared to 2.1% in first and second trimesters, p<0.001). Seven of 714 women with VUE (0.98%) had one or more recurrences of the condition within the study period. Of these, VUE was of lower grade in two of the three women who were prescribed aspirin in the subsequent pregnancy. Furthermore, basal VUE without basal myometrial fibres (6.6%), was over-represented among clinically morbidly adherent placentas (MAP) reported in this cohort. Our study does not show evidence of a seasonal variation in VUE incidence. The immune-mediated pathogenesis of VUE is favoured, with our data showing increased rates of the condition as maternal age increases.