Chorionic biopsy: what it is, what it is for and when it is done 2026

Chorionic labiapsy.

It is a test that is usually carried out between weeks 10 and 13 of pregnancy, although some sources indicate that it is also possible to perform it after 8 weeks. However, between weeks 10 and 12 of pregnancy it is usually more common for it to be carried out.

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What is chorionic biopsy? How is it done?

Also known medically as chorionic villus sampling, or chorionic villus biopsy, it is a medical test that determines whether a fetus is at risk for birth defects.

That is, it is a useful prenatal test to verify, or rule out, the existence of hereditary diseases or chromosomal disorders in a fetus.

To do this, during the procedure the doctor takes a sample of the chorionic villi, a tissue found in the placenta, and which has really valuable information, since it contains information about the baby's genes. That is, this sample of placenta tissue shares the same genetic makeup as the still-developing baby.

The sample can be taken through the cervix, or by inserting a needle through the abdominal wall, in order to obtain enough tissue to perform the test.

In this way, the genetic information present in the tissue is used from a medical point of view to determine if an abnormal biochemical or genetic condition exists.

What is chorionic biopsy used for?

The goal of chorionic biopsy is to determine if the developing fetus has or presents certain defects. In particular:

Chromosomal abnormalities

Some of the most common chromosomal abnormalities, which this test is capable of detecting, are:

• Down syndrome. It is a condition in which the child is born with an extra copy of his or her chromosome 21, hence it is also known as trisomy 21. This causes delays and disabilities in both physical and mental development.
• Other trisomies. Such could be the case of Patau syndrome (trisomy 13), Warkany syndrome (trisomy 8), trisomy 16, trisomy 22 or trisomy 9.
• Turner syndrome. It is a chromosomal disorder that affects only women, and involves the lack of part or all of a second sex chromosome in some or all of the cells. It is also known as syndrome X, syndrome 45 or Ullrich-Turner syndrome.
• Klinefelter syndrome. It is a chromosomal condition that can affect physical and intellectual development, in which there is the presence of an extra X chromosome in the cells.

Genetic disorders

Some of the most common genetic disorders are:

• Cystic fibrosis. This is a hereditary disease that mainly affects both the lungs and the digestive system (especially the pancreas). The body produces thick, sticky mucus that can clog the lungs and pancreas.
• Fragile X syndrome. It is a disease that affects a child's learning, appearance, behavior and health. Symptoms can be mild or severe, with boys usually having a more severe form than girls.
• Huntington's disease is an incurable inherited brain disorder that causes damage to neurons (brain cells) as a result of a defective gene that causes toxic proteins to accumulate in the brain.

When is the chorionic biopsy done?

Not all pregnant women need this test. Generally, a chorionic biopsy is performed when there is a possibility that the fetus has some type of abnormal condition. Therefore, a doctor may consider it useful - and necessary - to perform it in some circumstances, such as:

• The woman is over 35 years old. Women over 35 years of age have a higher risk of having children with chromosomal abnormalities.
• The pregnant woman or her partner has some type of genetic disorder.
• The pregnant woman or her partner has a family history of a genetic disorder.
• The woman has had other children with biochemical or genetic disorders.

It may also be indicated when the pregnant woman has had several spontaneous abortions, and when the results of prenatal screening tests have been abnormal.