Localized Placental Mesenchymal Dysplasia in Monochorionic Diamniotic Twin Placenta with Beckwith-Wiedemann Syndrome.

Placental mesenchymal dysplasia (PMD) is often associated with Beckwith-Wiedemann syndrome. A 27-year-old woman with preeclampsia prematurely delivered twin girls. One side of the placenta was larger with numerous grape-like vesicles, histologically with large, cystic, stem villi with cisterns without syncytiotrophoblastic hyperplasia. This side showed mosaicism for chromosome 11 by FISH and hypomethylation at ICR2 by MLPA. The smaller side of the placenta was normal macroscopically, microscopically, and karyotypically. There was symmetric growth restriction, macroglossia and hypoglycemia of the girl corresponding to the abnormal placental side, and lesser symmetric growth restriction and mild hypoglycemia in the other girl. Localized placental mesenchymal dysplasia can occur in monochorionic diamniotic twin placenta with Beckwith-Wiedemann syndrome. Fetal affects may be asymmetric. PMD can be associated with mosaicism monosomy of chromosome 11.