The role of perinatal pathological examination in subclinical infection in obstetrics.

Infectious agents are associated with a wide range of obstetric complications and pathological processes affecting the placenta, membranes and fetus. In some cases there will be associated maternal symptoms and signs indicating an infectious aetiology, but in the majority such infection is subclinical, and specific diagnosis or confirmation is achieved following pathological examination of the delivered placenta and/or fetus. There are two major groups of microorganism-related mechanisms associated with significant perinatal morbidity and mortality. First, ascending genital-tract infection, almost always bacterial, which ranges from localized choriodecidual inflammation to frank chorioamnionitis with fetal sepsis; this is a major cause of mid-trimester miscarriage and severe preterm delivery, and more recent data suggest that it may also have potentially important effects via cytokine release mediating neonatal cerebral injury. Second, haematogenous spread of maternal systemic infection--bacterial, viral or parasitic--which may result in isolated placental effects or transmission to the fetus with associated developmental abnormalities and neonatal complications. In many cases distinctive histopathological findings are described, and in addition a wide range of techniques is now available for culture and microscopy to confirm these diagnoses; such techniques include highly specific immunohistochemical markers and sensitive molecular diagnostic techniques such as the polymerase chain reaction. It is likely that with increasingly widespread availability of these investigative approaches to obstetric pathology, a greater understanding of the role of infectious agents in obstetric complications will become apparent.