Mesenchymal dysplasia of the placenta

Abstract
A severe case of placental mesenchymal dysplasia occurred in association with intrauterine fetal death (IUFD). The gravida‐1, para‐1 mother was a 26‐year‐old Japanese. The first pregnancy was unremarkable and a healthy female infant was delivered. The present pregnancy had been uneventful until 34 weeks of gestation when IUFD was detected. The 1516‐g (mean ± SD, 2050 ± 387 g) stillborn infant had no external abnormalities and the karyotype was 46,XX. The placenta was markedly enlarged (1050 g; mean ± SD, 452 ± 202 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, fetal vessels. There was no abnormal trophoblastic proliferation. Large‐sized fetal vessels in the chorionic plate frequently contained organized thrombi. This is the first case of placental mesenchymal dysplasia, which possibly lead to the IUFD.