Abstract
Twenty-one placentae from uncomplicated pregnancies of rhesus macaques in the third trimester (124–164 days) were examined to determine placental incidental lesions. Placental weight (PW) generally correlated with fetal weight (FW); PW:FW equaled approximately 1:3. Most placentae were bidiscoid (9.5% monodiscoid) with eccentric cord insertion and marginal or circummarginate membrane insertion. Macroscopically, there was in varying degrees, subchorionic, perivillous, and perilobular fibrin deposition, focal infarction, retroplacental hematoma, and calcification. Histologic changes included fibrinoid necrosis of villi, multifocal acute inflammation, excessive cytotrophoblasts, formation of syncytial knots, and intimal proliferation in umbilical vessels. Volume density of fibrinoid necrosis and calcification in terminal villi showed nonstatistically significant increases to term. However, calcification in reference to entire placental tissue increased significantly to term. All lesions seen in the rhesus are also seen incidentally in human placentae, but may become significant in correlation with pregnancy wastage if present to a large degree.