Mesenchymal dysplasia of the placenta

A severe case of placental mesenchymal dysplasia occurred in association wi th intrauterine fetal death (IUFD). The gravida-1, para-1 mother was a 26-y ear-old Japanese. The first pregnancy was unremarkable and a healthy female infant was delivered. The present pregnancy had been uneventful until 34 w eeks of gestation when IUFD was detected. The 1516-g (mean +/- SD, 2050 +/- 387 g) stillborn infant had no external abnormalities and the karyotype wa s 46,XX. The placenta was markedly enlarged (1050 g; mean +/- SD, 452 +/- 2 02 g), and approximately 80% was occupied by extraordinary enlarged villous structures with a myxoid appearance. Histologically, the dysplastic villi had myxoid stroma and a decreased number of, occasionally obliterated, feta l vessels. There was no abnormal trophoblastic proliferation. Large-sized f etal vessels in the chorionic plate frequently contained organized thrombi. This is the first case of placental mesenchymal dysplasia, which possibly lead to the IUFD.