Study participants
All term deliveries in the Stockholm Region between January 1st 2014 and August 31st 2020 complicated by chorioamnionitis, defined as a registered diagnosis in the Swedish pregnancy register (ICD-10 O41.4) were identified. From these, a random sample of 500 was identified and made up the study population. Recently, an expert panel of maternal and neonatal experts recommended dividing chorioamnionitis into the three separate categories ‘Isolated maternal fever’, ‘Suspected chorioamnionitis’, and ‘Confirmed chorioamnionitis’ (Supportive information, eTable 1)(2). Based on this categorization, and for the purpose of this study, ‘Isolated maternal fever’ is defined as at least 1 registered maternal temperature between 38.0°C and 38.9°C, and no additional signs of infection. ‘Suspected chorioamnionitis’ is defined as i) ≥ 1 registered maternal temperature ≥ 39.0°C or ii) ≥ 1 registered maternal temperature between 38.0°C and 38.9°C in combination with at least one clinical sign of infection of: fetal tachycardia (>160 beats per minutes [bpm] for 10 minutes or longer), maternal leukocytosis (leucocyte count >15,000 cells/mm3), or purulent discharge from the cervical os. ‘Confirmed chorioamnionitis’ is defined as i) a positive culture from cervix or amniotic fluid, confirming the presence of bacteria or ii) placental histopathological changes typical for chorioamnionitis. The registered chorioamnionitis diagnosis in the Swedish Pregnancy Register has not previously been validated, wherefore we validated the chorioamnionitis diagnoses of the study cohort against medical chart information. In total, 49 (9.8%) fulfilled the criteria of isolated maternal fever, 397 (79.4%) of suspected chorioamnionitis and 151 (30.2%) of confirmed chorioamnionitis. The corresponding positive predictive value of chorioamnionitis overall was excellent (0.92 [95% CI 0.89-0.94]) (Supportive information eMethods 1 and eTable 2).