This is a high-precision diagnostic procedure aimed at detecting possible genetic abnormalities and congenital diseases in the early stages of fetal development by examining the chromosomal set of chorionic cells.
The chorion is the outer villous membrane of the fetal egg, which by the 16th week of pregnancy is transformed into the placenta, which provides nutrition to the fetus
The chorionic villi chromosome set corresponds to the fetal chromosome set – therefore, a genetic study of chorionic villi can detect chromosomal abnormalities in the fetus
93% – accuracy of analysis of genetic material extracted from chorionic villi
9-12 weeks of pregnancy is the optimal period for chorionic biopsy
When is a chorionic biopsy procedure prescribed?
- the mother’s age is 35 years and older
- chromosomal rearrangements or aneuploidies on the sex chromosomes of the parents
- birth of a child with a chromosomal pathology in the family
- Identification of carriers of family chromosomal abnormalities
- monogenic diseases that were previously detected in the family and in the closest relatives
- results of the mother’s blood serum test, which indicates an increased risk of chromosomal abnormality in the fetus
- fetal anomalies detected during ultrasound examination
- If a woman took a number of pharmacological drugs (anticancer and other) before or during pregnancy
- past viral infections (hepatitis, rubella, toxoplasmosis, etc.)
- exposure of one of the spouses before conception
- at least two spontaneous abortions in the early stages of pregnancy in the past
The age of a pregnant woman over 35 years increases the risk of developing Down syndrome in a child
- 1 case out of 350 pregnancies in women over 35
- 1 case out of 100 pregnancies in women over 40
Genetic diagnostics of chorionic villi can detect various chromosomal abnormalities:
- trisomies on autosomes and sex chromosomes
- monosomies on autosomes and sex chromosomes
- cases of polysomy on the sex chromosomes
- polyploids
- Structural chromosomal abnormalities (translocations) presence of marker chromosomes
- combined variants of chromosomal pathology
A chromosomal abnormality can be presented:
- changes in the number of chromosomes (aneuploidy, for example, the absence of one of the chromosomes or, conversely, the appearance of an additional chromosome in the karyotype)
- violation of their structure (for example, due to insertion (duplication) or loss (deletion) of a certain part of the chromosome)
- exchange of genetic material between different chromosomes
Stages of chorionic biopsy
- Determination of the location of the chorion and fetus under the control of an ultrasound machine
- Introduction of a special puncture needle or catheter into the chorion – through the vagina and cervix or abdominally
- Taking a sample of chorionic villi cells
- Conducting a cytogenetic (molecular genetic) study of chorionic cells
The chorionic biopsy procedure does not require general anesthesia.
Despite the fact that a puncture occurs, it is practically imperceptible, but discomfort is possible.
Types of genetic testing of chorionic villi
Cytogenetic testing
This method determines the presence of additional or missing chromosomes (for example, Down syndrome – extra 21st chromosome, Klinefelter’s syndrome – extra X chromosome, Turner’s syndrome – lack of X chromosome in a female fetus)
Cytogenetic testing (karyotyping)
It is a study of the chromosome set by means of specific G-staining of maximally condensed chromosomes during the metaphase of mitotic cell division and analysis of the number and structure of chromosomes under a microscope
In standard karyotyping, it is considered sufficient to analyze 11 metaphase plates.
Molecular cytogenetic study (FISH analysis – fluorescent in situ hybridization)
A method that identifies a specific chromosome or part of a chromosome in the material under study.
If it is technically impossible to determine the complete karyotype of the embryo/fetus from the provided material, a molecular cytogenetic FISH analysis is performed to determine the number of 21, 13, 18, X and Y chromosomes.
Molecular genetic research
This method determines the presence of defects inside chromosomes, i.e. the presence of gene mutations that cause certain diseases: hemophilia, phenylketonuria, Duchenne muscular dystrophy, cystic fibrosis.
Cytogenetic testing is considered the “gold standard” for the diagnosis of any aneuploidy (i.e., quantitative changes in chromosome number), including confirmation or exclusion of syndromes:
- Down’s disease (trisomy 21)
- Edwards (trisomy 18)
- Patau (trisomy 13)
- Klinefelter’s disease (an extra X chromosome in a man),
- Shereshevsky-Turner (deficiency of one X chromosome in a woman)
- others.
Results of chorionic biopsy
Negative
Means that the fetus has no abnormalities in the number and structure of chromosomes
Positive.
It means that the fetus has abnormalities in the number and structure of chromosomes.
It is the basis for making decisions on:
- preservation of pregnancy
- Preparing yourself and your family for the birth of a child with developmental disabilities
- delivery in a specialized obstetric hospital.
Please note!
Biopsy of chorionic villi increases the risks:
- miscarriage
- bleeding
- infection of the fetus
- unfavorable course of pregnancy in case of Rh conflict.
In the case of a rhesus conflict, the body of a rhesus-negative mother produces antibodies that destroy the fetus’s red blood cells.
A chorionic biopsy can stimulate the production of antibodies.
What are the risks of ignoring a chorionic villus biopsy recommended by a doctor?
- the risk of having a child with one of the birth defects
- the birth itself becomes a risk group, since the doctor delivering the baby does not know about possible congenital pathologies
- childbirth can take place in a maternity hospital where there are no proper conditions for resuscitation of newborns and premature babies
- moral unpreparedness for the birth of a child with a serious illness or birth defect
- 0.8 – 2% – risk of complications of transabdominal biopsy of chorionic villi
- the likelihood of complications increases if the test is performed by an insufficiently qualified doctor
You should make an appointment for a fetal chorionic villus biopsy if:
- you will be 35 years old at the time of conception and are concerned about the increased risk of possible genetic abnormalities in the fetus
- you believe that it is more important to know about abnormalities in fetal development than to constantly worry about a possible miscarriage
- there have been cases of birth defects in your family or partner that can be detected by a chorionic villus biopsy
- you or your partner is a carrier of a hereditary disease or chromosomal defect that can be inherited by a child
- you want to find out as early as possible whether there are abnormalities in the development of the fetus, so that if the result is positive, you have time to make a decision: terminate the pregnancy or mentally prepare for the birth of a sick child
IMPORTANT!
- Specialists of theIVMEDclinic recommend consulting a doctor about the need to diagnose chorionic villi.
- The decision to conduct the test is made by the family based on the information provided by the doctor.
- The doctor recommends the test only if the risk of severe disease in the fetus exceeds the risk of complications from invasive diagnostics.
Carrying out the procedure
- 20 minutes – preparation and biopsy time
- There are 2 ways to perform a chorionic biopsy:
- transabdominal – taking tissue samples through the anterior abdominal wall with anterior chorionic position
- transcervical – taking tissue samples through the vagina and cervix with a posterior chorionic position
- 7-10 days – the results of the study of the genetic material of chorionic villi are ready
