Strengths and Limitations
This study has multiple strengths. Firstly, the population-based approach of identifying the study population naturally minimize the risk of selection bias. We could include the majority of cases with chorioamnionitis at term gestation in the region of Stockholm, accounting for 25% of all deliveries in Sweden, during the study period. Secondly, the Swedish Pregnancy Register contains prospectively collected detailed information from the pregnancy and postpartum period, which precludes the risk of recall bias. Specific clinical information was extracted retrospectively from medical charts, but the information on neonatal outcomes was added separately after the medical chart review, why we regard the risk of recall bias as minor. Thirdly, our validation of registered chorioamnionitis diagnosis against medical chart data revealed an excellent validity ensuring the internal study validity. Despite of these methodological advantages, our results should be interpreted in the light of some potential study limitations. The validity of neonatal diagnoses in the Swedish Pregnancy Register has not been assessed. There may be cases of delayed presentation of adverse neonatal outcomes, which might not be captured by the Swedish Pregnancy Register, potentially leading to an overall underestimation of adverse neonatal outcomes. It is possible that there were patients with chorioamnionitis who were misdiagnosed (false negative) during the study period, and consequently not included in the study. Finally, the regional cohort makes it difficult to fully extrapolate our results to other settings due to potential differences in demographic characteristics among pregnant women between regions and countries, and different diagnostic traditions. We do however think that our main findings – an association between specific signs of chorioamnionitis and neonatal complications – may be generalizable to other populations.