Objective: To investigate whether conisation increases chorioamnionitis (CAM) and assess whether this risk differs between preterm and term periods. Furthermore, we estimated mediation effects of CAM between conisation and preterm birth (PTB).
Design: A nationwide observational study.
Setting: Japan.
Population: Singleton pregnant women derived from the perinatal registry database of the Japan Society of Obstetrics and Gynaecology between 2013 and 2019.
Methods: The association between a history of conisation and clinical CAM was examined using a multivariable logistic regression model with multiple imputation. We conducted mediation analysis to estimate effects of CAM on PTB following conisation.
Main outcome measures: Clinical CAM.
Results: Of 1 500 206 singleton pregnant women, 6961 (0.46%) underwent conisation and 1 493 245 (99.5%) did not. Clinical CAM occurred in 150 (2.2%) and 11 484 (0.8%) women with and without conisation, respectively. Conisation was associated with clinical CAM (odds ratio [OR] 3.09; 95% confidence interval (CI) 2.63-3.64; p < 0.001) (risk difference 1.57%; 95% CI 1.20-1.94). The association was detected among 171 440 women with PTB (OR 3.09; 95% CI 2.57-3.71), whereas it was not significant among 1 328 284 with term birth (OR 0.88; 95% CI 0.58-1.34). OR of total effect of conisation on PTB was 2.71, OR of natural indirect effect (effect explained by clinical CAM) was 1.04, and OR of natural direct effect (effect unexplained by clinical CAM) was 2.61. The proportion mediated was 5.9%.
Conclusions: Conisation increased CAM occurrence. Obstetricians should be careful regarding CAM in women with conisation, especially in preterm period. Bacterial infections may be an important cause of PTB after conisation.
Keywords: cervical conisation; cervical intraepithelial neoplasia; chorioamnionitis; preterm birth; preterm premature rupture of membrane.
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