The most common lesion of a mature placenta with no much clinical significance is:

Chorionic villi receive oxygen solely from maternal circulation through the uteroplacental vessels, which jet blood into the intervillous space. Uteroplacental diseases that diminish or obstruct this connection can lead to villous infarction. Although these are common lesions in mature placentas, if they are numerous, placental insufficiency may develop. When they are thick, centrally located, and randomly distributed, they may be associated with preeclampsia or lupus anticoagulant. Striking enlargement of the chorionic villi is commonly seen in association with severe erythroblastosis and fetal hydrops. It also has been described in maternal diabetes, fetal congestive hea failure, and maternal-fetal syphilis. Large retroplacental, marginal, and subchorial hematoma (also known as Breus mole) have been associated with higher rates of miscarriage, abruption, fetal-growth restriction, preterm delivery, and adherent placenta. Ref: Leveno K.J., Hauth J.C., Rouse D.J., Spong C.Y. (2010). Chapter 27. Abnormalities of the Placenta, Umbilical Cord, and Membranes. In K.J. Leveno, J.C. Hauth, D.J. Rouse, C.Y. Spong (Eds), Williams Obstetrics, 23e.