**11. Placental membranes**

The fetal membranes (chorion, amnion) represent the interface between the fetal graft and the maternal host [1]. Infection may also pass the fetal membranes, especially in the area overlying the cervix. It provides direct access to pathogens, ascending from the vagina and the cervix [62]. Less commonly, infectious agents enter the uterus as a result of invasive procedures (e.g., amniocentesis, fetoscopy, cordocentesis, and chorionic villus sampling) or via the fallopian tubes from an infectious process in the peritoneal cavity.

### **11.1. Chorioamnionitis**

Chorioamnionitis is the most frequent histopathological result of ascending transcervical infection and occurs with both symptomatic and silent infections [63]. The histologic diagnosis of chorioamnionitis is allowed if the inflammatory infiltrate involves either or both the chorion and the amnion. The acute chorioamnionitis is more common than the chronic form [64]. As clinical symptoms, chorioamnionitis is characterized by maternal fever, tachycardia, uterine tenderness, or foul-smelling amniotic fluid. However, cultures of the amniotic fluid or membranes fail to document the bacterial infection in 25–30% of placentas with histologic chorioamnionitis [65]. The infection of the membranes is often polymicrobial, with the most commonly seen bacteria: *Streptococcus* sp., *Escherichia coli*, *Ureaplasma* sp., *Fusobacterium* sp., *Mycoplasma* sp., and anaerobes [63]. The correct diagnosis and treatment of chorioamnionitis are paramount, as it is an important cause of perinatal and maternal morbidity and mortality [66]. The major pathological consequences of chorioamnionitis may include premature rupture of membranes, preterm labor, prolonged labor, premature delivery, fetal and newborn infection, and endomyometritis.
