The role of the placenta in feto-neonatal infections.

The placenta and membranes may be infected by ascending bacteria from the maternal birth canal or by bacteria, virus and protozoa via haematogenous spread. The maternal and fetal inflammatory reactions, elicited by these microorganisms, are often associated with precise anatomo-pathological findings. Furthermore, it has been demonstrated a strong relationship between placental inflammation and important perinatal adverse outcomes, including neurologic impairment and chronic lung disease. For this reason, placenta examination is an important approach for understanding infection and/or inflammation leading to fetal inflammatory response syndrome. For instance, chorioamnionitis caused by ascending infections are characterized mainly by polymorphonuclear leucocytic infiltration of the extraplacental membranes, firstly involving the lower-pole of the amniotic sac, then the intervillous space and later the chorionic plate. In fact, there is an initial "maternal inflammatory response" (MIR) to the infection and leucocytes migrate from the maternal blood stream. Subsequently, the chorionic plate is infiltrated by leucocytes derived from the fetal vessels, and this event characterizes the "fetal inflammatory response" (FIR). The release of proinflammatory cytokines and chemokines within the gestational sac is the leading cause of fetal and neonatal damage. In conclusion, certain placental reaction patterns may identify and estimate the risk for specific perinatal complications in infants.