Chimeric Singleton Placenta Comprising Placental Mesenchymal Dysplasia and Complete Hydatidiform Mole with Live Birth and Postpartum Diagnosis of Gestational Trophoblastic Neoplasia

Placental mesenchymal dysplasia (PMD) is a benign lesion that is often misdiagnosed as complete (CHM) or partial hydatidiform mole. PMD usually results in live birth, but can be associated with several fetal defects. Herein, we report PMD with CHM in a singleton placenta with live birth.A 34-year-old gravida 2, para 1, living 1 (G2P1L1) woman was referred on suspicion of a molar pregnancy in the first trimester. msHCG levels were increased during early pregnancy, with multicystic lesions and placentomegaly observed on ultrasonography. Levels decreased to normal with no fetal structural abnormalities observed. A healthy male infant was delivered at 34 gestational weeks. Placental p57KIP2 immunostaining and short tandem repeat analysis revealed three distinct histologies and genetic features: normal infant and placenta, PMD, and CHM. Gestational trophoblastic neoplasia was diagnosed and up to fourth-line chemotherapy administered.Distinguishing PMD from hydatidiform moles is critical for avoiding unnecessary termination of pregnancy. CHM coexisting with a live fetus rarely occurs. This case is unique in that a healthy male infant was born from a singleton placenta with PMD and CHM.