A 36-year-old primigravida develops peripheral edema late in the second trimester. On physical examination, her blood pressure is 155/95 mm Hg. Urinalysis shows 2+ proteinuria, but no blood, glucose, or ketones. At 36 weeks, she gives birth to a normal viable but low-birth-weight infant. Her blood pressure returns to normal, and she no longer has proteinuria. Which of the following pathologic findings is most likely to be found on examination of the placenta?

Toxemia of pregnancy in this case is best classified as preeclampsia because she has hypertension, proteinuria, and edema, but no seizures. The placenta tends to be small because of reduced maternal blood flow and uteroplacental insufficiency; infarcts and retroplacental hemorrhages can occur. Microscopically, the decidual arterioles may show acute atherosis and fibrinoid necrosis. Chorioamnionitis is most often due to ascending bacterial infections and leads to, or follows, premature rupture of membranes. A chronic villitis is characteristic of a congenital infection such as cytomegalovirus. Placental hydrops often accompanies fetal hydrops in conditions such as infections and fetal anemias. In a partial mole, a fetus is present, but it is malformed and rarely live-born.