What is Trophoblast?

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  • Written By: Mary McMahon
  • Edited By: Kristen Osborne
  • Last Modified Date: 26 September 2019
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A trophoblast is a layer of cells comprising the outer shell of a blastocyst, a cellular cluster that will eventually develop into an embryo. The trophoblast plays an important role in embryonic implantation and development and the cells it contains are among the first to start differentiating as a fertilized egg begins dividing to produce an embryo. Ultimately, these cells develop into the placenta, the interface between fetus and mother designed to provide a conduit for nutrients and waste products.

Within four to six days after fertilization, the trophoblast begins to form. These cells arrange themselves along the outside of the developing blastocyst and begin secreting hormones designed to prepare the endometrium, the lining of the uterus, for implantation. Initially, the blastocyst drifts in the uterus, until the trophoblast successfully connects with the uterine lining and implants. The trophoblast can begin dividing and differentiating to create the placenta.

A number of things can go wrong in the early stages of embryonic development. Cells may fail to divide, stopping development in its tracks, or fatal errors of division may occur. Sometimes the blastocyst fails to implant and it will stop developing as a result of not being able to access nutrients. Once implanted, environmental exposures and a wide variety of other factors can interfere with successful development.


After delivery, the placenta is expressed and can be discarded. It is important to remove the entirety of the placenta from the uterus to limit the risks of infection and other complications related to retained placental material. There are also concerns about uterine bleeding and other complications after delivery, requiring follow up medical appointments to look for signs of complications.

Trophoblastic cells can become cancerous. Sometimes an embryo fails to develop and the trophoblastic cells continue dividing in a molar pregnancy, and if trophoblastic cells are left behind after delivery, they can develop into a trophoblastic tumor. Known as gestational trophoblastic disease, these abnormalities of cell development are sometimes benign and sometimes not. Biopsy of the cells is needed to learn more about the origins of the growth and their level of malignancy.

Like other cells involved in embryonic development, trophoblastic cells are a topic of interest for researchers. Scientists are interested in studying the way that cells signal between themselves as a fetus develops and they also look at what goes wrong with embryonic development. This research can be applied to infertility and a variety of other medical issues.


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