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.