Chorionic Biopsy

General Description

Chorionic biopsy is a prenatal test that examines chorionic villi (projections from one of the placenta's layers that facilitate the exchange of nutrients, oxygen, and waste between the mother and the embryo) to diagnose the presence of chromosomal abnormalities in the fetus. To provide accurate information, it must be performed between the 10th and 13th weeks of pregnancy, preferably during the 11th or 12th week. It is an invasive diagnostic procedure that allows for a cytogenetic, molecular, and biochemical study of the chorionic villi.

First, a placenta sample is obtained through an excision biopsy (removing a cylindrical or wedge-shaped tissue fragment) or aspiration (suctioning with a needle and syringe). After processing and studying the sample in the laboratory, preliminary information is available within 48 hours, while definitive results require a culture that takes approximately one week.

The chorionic villus biopsy allows for an early cytogenetic (chromosomal) study of the fetus. It provides a definitive diagnosis of Down syndrome and can detect various genetic or metabolic diseases, though it cannot determine the presence of congenital abnormalities that are not of chromosomal origin.

When Is It Indicated?

Chorionic biopsy is indicated when there is a high risk that the fetus may inherit genetic diseases or have chromosomal abnormalities. It is recommended in the following cases:

• Advanced maternal age (over 35 years).
• Family history of chromosomal disorders.
• Chromosomal abnormality markers detected during routine ultrasound.
• Signs of Down syndrome in previous tests.
• Detection of malformations in prior ultrasounds.
• Risk of genetic, metabolic, or biochemical diseases such as muscular dystrophies, hemophilia, or fragile X syndrome.
• Part of a paternity test.

This type of biopsy is not recommended before the 10th week of pregnancy or in cases of sexually transmitted infections, particularly in patients with hepatitis (B or C) or HIV with a high viral load.

How Is It Performed?

The sample collection method varies depending on the technique used:

• Transcervical chorionic biopsy: This is the most common procedure, as it allows for a larger tissue sample. The placenta is accessed through the vagina and cervix with the aid of an ultrasound. The tissue is collected using forceps or a suction catheter.
• Transabdominal chorionic biopsy: After disinfecting the area with an iodine solution, a puncture is made in the abdomen with a hollow needle through which the necessary instruments are inserted to obtain the sample.
• Transabdominal aspiration with a syringe: Similar to amniocentesis, which is used to analyze a sample of amniotic fluid, a fine needle is inserted into the most suitable area of the abdomen after assessing the position of the placenta and fetus via ultrasound. The syringe plunger is then used to obtain the necessary tissue.

Before examining the sample under a microscope, it is fixed with formaldehyde (CH₂O) to prevent decomposition and sealed to avoid oxidation. The material is then cut into thin layers and placed on a glass slide. Staining techniques may be used to better define cellular structures, making them more visible under the microscope. This analysis assesses the shape, size, and number of fetal chromosomes.

Risks

Chorionic villus biopsy is an invasive technique that can cause premature rupture of the amniotic membrane or an infection of the amniotic fluid. Additionally, although the risk has been reduced thanks to greater medical specialization, miscarriage can occur after the procedure (less than 1%).

What to Expect from a Chorionic Biopsy

On the day of the procedure, it is advisable to wear comfortable clothing, as you will need to undress and wear the gown provided at the medical center. Before the test, an informed consent form must be signed.

For a transcervical biopsy, the patient must be in the gynecological position—lying on the examination table with legs apart and placed in stirrups. The specialist then inserts a speculum to keep the vagina open and facilitate the insertion of the necessary instruments to collect the sample. If a transabdominal biopsy is performed, the patient remains semi-reclined on the table with the abdomen exposed. In both cases, the process is guided by an abdominal ultrasound.

Depending on the individual, the chorionic biopsy may be painless or cause a slight prick or pain similar to menstrual cramps when the sample is taken.

To avoid complications, absolute rest is recommended for 24 hours after the procedure. Additionally, strenuous activities should be avoided, and relative rest should be observed for 72 hours after the biopsy. Therefore, it is advisable to attend the procedure with a companion.

Some discomfort or a bruise may appear at the puncture site. It is essential to seek emergency medical attention if vaginal bleeding occurs, amniotic fluid leaks, sharp pain is felt, or fever develops.

Preliminary short-culture results are available within 48 hours, but complete results take several days.

Specialties That Request a Chorionic Biopsy

Gynecologists, obstetricians, and geneticists are the specialists who typically request this type of prenatal test.