What Is Chorionic Villi? - Sampling & Definition

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  • 0:01 Definition of Chronic Villi
  • 1:00 Chorionic Villi Sampling
  • 2:25 Lesson Summary
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Lesson Transcript
Derrick Arrington

Derrick has taught biology and chemistry at both the high school and college level. He has a master's degree in science education.

Expert Contributor
Ana Benito Gonzalez

Ana has a PhD in Biology. She has taught college classes at leading U.S. universities, also works as a Biology tutor. She has published several scientific journals.

Chorionic villi form during pregnancy and are crucial in the diagnosis of many illnesses that could affect a baby. In this lesson, we'll examine what makes up chorionic villi as well as how they're used in the field of medicine.

Definition of Chorionic Villi

When a fetus is developing, it has many membranes that link it to the mother. One of those membranes is known as the chorion. The chorion is formed by mesoderm tissue from the mother and trophoblast cells derived from the forming fetus. The chorionic villi emerge from this chorion and enter the endometrium. Chorionic villi are microscopic, finger-like projections that contain capillaries for blood to flow through. The endometrium is the inner membrane of the uterus. It is here that the chorionic villi allow the transfer of nutrients from the mother's blood to the fetus.

Embryonic blood is carried to the villi by the various branches of the umbilical arteries. Here, the blood circulates through the capillaries of the villi and is then returned to the fetus through the umbilical veins. Oxygen and nutrients from the mother's blood diffuse through the walls of the villi to, and provide nourishment for, the growing fetus. Carbon dioxide and waste products from the fetus circulate through the villi back into the mother's blood.

Chorionic Villi Sampling

Chorionic villi sampling is a test done during early pregnancy that can detect problems with the fetus. While it is becoming more and more commonplace in medicine today, it traditionally was only performed when there were risk factors for the fetus. These risk factors may include increased age of the parents or a history of genetic disease.

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Additional Activities

Role Play Activity

The chorionic villi are made of a series of blood vessels that help to transfer nutrients and oxygen from the mother's bloodstream to the future baby throughout pregnancy. Imagine you are a doctor, and you have a pregnant woman in your office that needs a chorionic villi sampling. The reason she needs a chorionic villi sampling is because she is 35 and there is a genetic disease that runs in her family that leads to chromosomal abnormalities. She is currently 10 weeks pregnant. She is a first-time mom, and she is very nervous. Answer the following questions for her.

  1. What is the chorionic villi?
  2. Why do I need chorionic villi sampling?
  3. What are the advantages between chorionic villi sampling and an amniocentesis?


  1. Chorionic villi is a membrane full of blood vessels that surrounds the embryo. This membrane allows the exchange of nutrients and oxygen and waste and carbon dioxide between the mother and the fetus.
  2. She needs the chorionic villi sampling done because of her age and the fact that she has a history of chromosomal abnormalities running in her family. The test is optional, but in her case, is recommended by the doctors.
  3. The advantage of the chorionic villi sampling is that it can be done any time after 10 weeks of pregnancy. She would have to wait until around week 20 for an amniocentesis.

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