Role of the Placenta in Preterm Birth: A Review.

Preterm birth is a multifactorial syndrome with a variety of risk factors and long-term health consequences for the child. Placental pathology provides important diagnostic information to ascertain the cause of preterm birth. For example, intra-amniotic infection is one risk factor, but accumulating evidence based on placental pathology, amniotic fluid cultures, and polymerase chain reaction studies suggests infection may be a less common cause of preterm birth than previously suspected, especially after 32 weeks' gestation. Instead, many cases of spontaneous preterm labor leading to preterm birth appear to be caused by placental insufficiency, similar to preeclampsia and fetal growth restriction. Other causes of preterm birth, including retroplacental abruption, chronic villitis, and twin gestations, also have specific placental pathology related to placental insufficiency. New insights into the underlying mechanisms regulating uteroplacental blood flow and the impact of placental malperfusion on placental health may lead to improved early gestation diagnostic testing and a revolution in preventative care for both the mother and her child.