Chorioamnionitis is defined as inflammation of the amniochorionic (fetal) membranes of the placenta, typically in response to microbial invasion (Menon et al 2010). Chorioamnionitis occurs in 1% of livebirths (Monif and Baker 2004). The incidence of chorioamnionitis in preterm prelabour rupture of the membranes (PPROM) is 30%.
96% of cases are due to ascending infection, the remainder arise from haematogenous dissemination due to maternal septicaemia. Chorioamnionitis is usually polymicrobial. The most common causes of chorioamnionitis are mycoplasmas, E. coli, group B streptococci and anaerobic bacteria.
Monif GRG, Baker DA (editors). Infectious Diseases in Obstetrics and Gynecology. 5th ed. London: Parthenon. 2004. p 355–69.
Risk factors
Risk factors for chorioamnionitis include:
- prolonged membrane rupture (including PPROM)
- prolonged labour
- multiple digital examinations with membrane rupture
- nulliparity
- infection (group B streptococcus colonisation; bacterial vaginosis)
- alcohol and tobacco use
- meconium-stained amniotic fluid
- internal monitoring
- epidural anaesthesia.
Tita ATN, Andrews WW. Diagnosis and management of clinical chorioamnionitis. Clin Perinatol 2010;37:339–54.