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Intra-amniotic infection (clinical chorioamnionitis or triple I)

Alan Thevenet N Tita, MD, PhD
Section Editor
Vincenzo Berghella, MD
Deputy Editor
Vanessa A Barss, MD, FACOG


Historically, infection of the chorion, amnion, or both was termed "chorioamnionitis." Although this term remains in common use, the term "intra-amniotic infection" (IAI) is also commonly used since infection often involves the amniotic fluid, fetus, umbilical cord, or placenta as well as the fetal membranes. Adding to the complexity, the term "histologic chorioamnionitis" has been used to describe cases without the typical clinical or microbiological findings associated with acute infection. These cases may be the result of sterile inflammation or use of insensitive microbiologic techniques.

In 2015, a National Institute of Child Health and Human Development Workshop expert panel recommended use of the term “triple I” to address the heterogeneity of this disorder (table 1) [1]. The term triple I refers to intrauterine infection or inflammation or both and is defined by strict diagnostic criteria (see 'Diagnostic criteria' below), but this terminology has not been universally adopted [2].


Migration of cervicovaginal flora through the cervical canal is the most common pathway to IAI. Uncommonly, the pathway to IAI is hematogenous as a result of maternal bacteremia (eg, Listeria monocytogenes) infecting the intervillous space or from contamination of the amniotic cavity as a result of an invasive procedure (eg, fetoscopy). Infection from the peritoneum via the fallopian tubes has also been postulated but is likely rare [3]. Subsequent activation of the maternal and fetal inflammatory response systems generally leads to labor and/or rupture of membranes. (See "Pathogenesis of spontaneous preterm birth".)

Local host factors likely play a role in facilitating or preventing infection. The cervical mucus plug, membranes, and placenta provide barriers to ascending and transplacental infection, while rupture of membranes removes barriers. There is some evidence that the fetal membranes have antimicrobial activity [4,5]. Cells within fetal membranes appear to mediate innate immune responses through activation of toll-like receptors, key modulators of the innate immune response that recognize components of bacteria and viruses [6,7]. Lactobacilli in the vagina may induce changes in the flora that impair the virulence of pathogenic organisms.


The reported incidence of IAI in the United States varies widely among publications [8]. The variation is due to several factors, including differences in ascertainment (prospective studies report higher rates than retrospective studies), differences in prevalence of risk factors in the populations studied, use of different diagnostic criteria (eg, clinical versus histologic), and temporal changes in obstetric practice [9-11].

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Literature review current through: Oct 2017. | This topic last updated: Sep 27, 2017.
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