Placental infections
- Lesion
Bacteria climbing from the vagina inflame the membranes and can start preterm labour; germs carried in the mother's blood inflame the villi instead.
What it is
Infection reaches the placenta by two routes. Ascending infection from the vagina and cervix is by far the most common; bacteria inflame the membranes (acute chorioamnionitis), often causing premature rupture of membranes and preterm birth, and the fetus responds with inflammation of its own cord and chorionic vessels. Hematogenous infection, from the mother's blood, inflames the villi: acute villitis with Listeria, and chronic villitis with the TORCH organisms such as cytomegalovirus, syphilis and toxoplasma. Chronic villitis can also be immune rather than infectious.
Structure
- Chorioamnionitis: cloudy, opaque membranes; neutrophils in the chorionic plate and membranes, then the amnion with necrosis.
- Funisitis: neutrophils in the walls of the umbilical vessels and Wharton jelly.
- Acute villitis (Listeria): villi destroyed by neutrophils, intervillous abscesses.
- Chronic villitis: lymphocytes and histiocytes in villous stroma; cytomegalovirus inclusions and plasma cells; syphilis with large hypercellular villi and necrotizing funisitis.
Step by step
- Bacteria from the vaginal flora ascend through the cervix, more so after membranes rupture.
- They infect the membranes and amniotic fluid; maternal neutrophils are recruited.
- Inflammatory mediators and prostaglandins weaken the membranes and trigger contractions: preterm rupture and preterm labour.
- The fetus inhales or swallows infected fluid and mounts its own inflammatory response, which can injure the brain and lungs.
- In hematogenous infection, organisms in the maternal blood reach the intervillous space and infect the villi directly.
Two routes of placental infection
| Feature | Ascending | Hematogenous |
|---|---|---|
| Frequency | Common | Less common |
| Organisms | Vaginal bacteria (group B streptococcus, E. coli, mycoplasmas) | Listeria, cytomegalovirus, syphilis, toxoplasma, rubella, Zika |
| Main lesion | Acute chorioamnionitis and funisitis | Villitis (acute or chronic) |
| Clinical result | Preterm rupture, preterm labour, neonatal sepsis | Growth restriction, congenital infection, stillbirth |
Clinical notes
- Chorioamnionitis is a leading cause of spontaneous preterm birth and of early neonatal sepsis.
- Pregnant women are advised to avoid foods that carry Listeria, such as unpasteurised dairy and ready-to-eat deli meats, because it crosses the placenta.
- Congenital syphilis remains a public-health problem in Latin America and leaves characteristic placental changes.
Test yourself
Think of the answer, then tap the question to see it.
Which route of placental infection is most common, and what lesion does it cause?
The ascending route from the vagina; it causes acute chorioamnionitis.
How do you tell the fetal inflammatory response from the maternal one?
Fetal neutrophils come from the umbilical and chorionic plate vessels (vasculitis, funisitis); maternal neutrophils come from the decidua and intervillous space into the membranes.
Which bacterium causes acute villitis with microabscesses after maternal bacteraemia?
Listeria monocytogenes.
Elsewhere in DurgiPedia
- Placenta
- Fetal membranes: amnion, chorion, yolk sac and allantois
- Neonatal immunity: maternal IgG and breast-milk IgA
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: About Group B Strep Disease | Group B Strep | CDC (Centers for Disease Control and Prevention, 2026); About Listeria Infection | Listeria Infection | CDC (Centers for Disease Control and Prevention, 2026).
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Representative model, for educational purposes only.