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J Matern Fetal Neonatal Med. 2019 Feb 27:1-8. doi: 10.1080/14767058.2019.1578745. [Epub ahead of print]

Early development of the human placenta and pregnancy complications.

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a Department of Obstetrics and Gynecology , Haukeland University Hospital , Bergen , Norway.
b Department of Public Health and Primary Health Care , University of Bergen , Bergen , Norway.
c Department of Internal Medicine, Section of Endocrinology , Haukeland University Hospital, University of Bergen , Bergen , Norway.
d Department of Pathology, Center for Pediatric and Pregnancy Related Pathology , Oslo University Hospital , Oslo , Norway.
e Department of Obstetrics and Gynecology , University of Arkansas for Medical Sciences , Little Rock , AR , USA.
f Department of Obstetrics and Gynecology , University of Mississippi Medical Center , Jackson , MS , USA.


An adequately sized placenta at a suitable site with appropriate depth and centripetal progression of implantation are the major factors for optimal fetal development. The cytotrophoblasts surround the blastocyst fuses at the site of the uterine attachment. This forms a second layer of multinucleated syncytiotrophoblasts that constitutes the inner epithelial boundary of the chorionic villous against the intervillous space. In a normal pregnancy, extravillous cytotrophoblasts (EVT) invade and obstruct the spiral arteries and remodel them. Vacuoles in the syncytial cell layer fuse and develop the intervillous space. The inner cell mass (embryoblast) gives rise to the umbilical cord and the mesenchyme in the chorionic villi. Vasculogenesis starts with the formation of hemangioblastic cords in this mesenchyme. The trophoblastic cell columns anchor the placenta. A variety of molecular pathways participate in the placentation process. Placental morphogenesis occurs mainly through complex cellular interactions between the chorionic villous and the extravillous cytotrophoblasts. The formation of the normal structure of the chorionic villi, syncytiotrophoblast layer and vasculature is essential for placental function, hormone production, and regulation of fetal growth. At each stage of placental development, genetic variants, exposure to infection, poor vascular function, oxidative stress, or failure of normal development can all lead to abnormal formation resulting in the clinical complications of pregnancy such as fetal growth disorders, neonatal neurologic abnormalities, placental adhesions, and inflammatory problems as well as maternal disease such as preeclampsia.


Blastocyst; cytotrophoblast; implantation; placenta; pregnancy complications; spiral artery; syncytiotrophoblast

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