Most obstetricians and pediatricians would agree that the examination of the placenta often helps to explain an abnormal neona tal outcome. As early as in 1892, Ballantyne wrote, A diseased foetus without its placenta is an imperfect specimen, and a description of a foetal malady, unless accompanied by a notice of the placental condition, is incomplete. Deductions drawn from such a case cannot be considered as conc- sive, for in the missing placenta or cord may have existed the cause of the disease and death. During intrauterine life the foetus, the membranes, the cord and the placenta form an organic whole, and disease of any part must react upon and affect the others. Similar thoughts were succinctly detailed in Price’s (1950) discussion of his concept of the prenatal biases as they affected twins. His contribution also admonishes us that placental study is a sine qua non for a more perfect understanding of fetal development. Despite all this understanding of the past and appreciation for plac- tal disease, great resistance still exists to perform the task of placental examination routinely. For many pathologists, therefore, the placenta has remained a mysterious organ.

Examination of the Placenta.- Macroscopic Features of the Delivered Placenta.- Microscopic Survey.- Placental Types.- Early Development of the Human Placenta.- Basic Structure of the Villous Trees.- Architecture of Normal Villous Trees.- Characterization of the Developmental Stages.- Nonvillous Parts and Trophoblast Invasion.- Involution of Placental Site: Retained Placenta.- Anatomy and Pathology of the Placental Membranes.- Anatomy and Pathology of the Umbilical Cord.- Placental Shape Aberrations.- Histopathologic Approach to Villous Alterations.- Classification of Villous Maldevelopment.- Erythroblastosis Fetalis and Hydrops Fetalis.- Transplacental Hemorrhage, Cell Transfer, Trauma.- Fetal Storage Disorders.- Maternal Diseases Complicating Pregnancy: Diabetes, Tumors, Preeclampsia, Lupus Anticoagulant.- Infectious Diseases.- Abortion, Placentas of Trisomies, and Immunologic Considerations of Recurrent Reproductive Failure.- Molar Pregnancies.- Trophoblastic Neoplasms.- Benign Tumors and Chorangiosis.- Multiple Pregnancies.- Legal Considerations.

Most obstetricians and pediatricians would agree that the examination of the placenta often helps to explain an abnormal neona tal outcome. As early as in 1892, Ballantyne wrote, A diseased foetus without its placenta is an imperfect specimen, and a description of a foetal malady, unless accompanied by a notice of the placental condition, is incomplete. Deductions drawn from such a case cannot be considered as conc- sive, for in the missing placenta or cord may have existed the cause of the disease and death. During intrauterine life the foetus, the membranes, the cord and the placenta form an organic whole, and disease of any part must react upon and affect the others. Similar thoughts were succinctly detailed in Price’s (1950) discussion of his concept of the prenatal biases as they affected twins. His contribution also admonishes us that placental study is a sine qua non for a more perfect understanding of fetal development. Despite all this understanding of the past and appreciation for plac- tal disease, great resistance still exists to perform the task of placental examination routinely. For many pathologists, therefore, the placenta has remained a mysterious organ.