Another method from the arsenal of prenatal diagnosis – The chorionic villus sampling, as well as the amniocentesis (amniocentesis), is an invasive – penetrating into the body – method of prenatal diagnosis. As a result, information about genetic changes and possible genetic damage to the baby can be obtained already at a relatively early point in the pregnancy.
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Which diagnoses does a chorionic villus biopsy allow?
Through the procedure, the physician gains cells from the so-called chorion, an early development stage of the suckler pie (the placenta ). After tissue collection, the cells are examined in the laboratory.
In contrast to amniocentesis, in which cell cultures have to be created and the actual analysis is only possible after about 14 days, the first results of a chorionic villus biopsy are already available after 24 hours.
The examination of the cell preparations provides information about the number of chromosomes – i.e., the genetic information – of the baby, its rough structure and any anomalies.
For example, changes in the number of chromosomes, including trisomy 21 – the Down syndrome – can be found or largely ruled out by a chorionic villus biopsy. By creating cell cultures, an analysis of the chromosome structure or individual genes is possible afterward.
The physician can thereby receive information on some hereditary muscle and metabolic diseases. These detailed results of a chorionic villus biopsy are analogous to amniocentesis at the earliest after two weeks.
What are the chorionic villi?
The chorion arises at an early stage of embryonic development. The fertilized egg cell divides rapidly, after a few days two different cell types have emerged. From the embryoblast develops the embryo, the actual child.
The trophoblasts produce the placenta and the umbilical cord later in the pregnancy. After the implantation of the early embryo into the uterine lining, the second type of cell tissue thickened first into the so-called chorion frondosum, which later fused with the maternal tissue and is a precursor of the placenta.
For this reason, the chorion quickly develops tree-like branches – this is how the chorionic villi developed. The cells of the chorionic villi, with a few exceptions, have the same chromosomal structure as the cells of the child itself and therefore allow conclusions to be drawn about changes in his genome.
In rare cases, so-called mosaic structures can be found in cells of the chorionic villi. Their genetic make-up is then not identical to the cells of the child. Since the doctor can not see a clear result in such a case, the next step will be an amniocentesis.
How is the procedure going?
The cells of the chorionic villi can be obtained in two different ways:
- In the case of a transabdominal chorionic villus sampling (performed through the abdominal wall), the physician guides a thin puncture needle through the abdominal wall of the pregnant woman to the placenta to extract a tissue sample from the chorionic villi. The course of the biopsy is monitored continuously by ultrasound. Transabdominal chorionic villus sampling is most commonly used in prenatal diagnosis.
- If the placenta is in an unfavorable position, the chorion cells are taken transcervical (through the cervix – cervix). A catheter is advanced through the vagina, cervix and cervix to the placenta. This method is less commonly used because it is unclear whether this results in a higher risk of miscarriage compared to transabdominal chorionic villus sampling.
The entire procedure takes no longer than half an hour; the actual cell removal has brought the pregnant woman in a few minutes behind. The procedure is, if anything, only a little painful. Nevertheless, the test can be very stressful for the mother, not least for psychological reasons.
Doctors then recommend a few days of rest. In the first 24 hours after the biopsy, there may be slight vaginal bleeding or pain, which is almost always harmless – a medical examination should be done for safety nevertheless.
The risk of miscarriage due to chorionic villus sampling is between 0.5 and 1 percent, which is slightly higher than with amniocentesis, where miscarriage statistically occurs in only 0.25 to 0.5 percent of all cases. Overall, it is very low.
Also, the doctor will recommend chorionic villus sampling only if the likelihood of genetic damage to the baby is greater than the risk of miscarriage.
For which pregnant woman is the examination suitable?
After evidence of pregnancy, the gynecologist discusses with the expectant mother and possibly also with her partner, whether and what measures of prenatal diagnosis from a medical point of view are recommended or should be made at the request of parents.
The medical recommendation is based on whether there is an increased risk of genetic stress. For example, a chorionic villus biopsy is suitable
- if there is a family predisposition for genetic defects in the case of a mother or father
- if the woman already has a child with a chromosome disorder
- in case of abnormalities during the ultrasound examination of the baby
- in pregnant women over 35 years.
Before deciding on the test, the doctor will advise the pregnant women in detail. Many pregnant women initially opt for a first-trimester screening, which is also possible between the 11th and 14th week of pregnancy.
This involves measuring the nuchal translucency and determining the status of two hormones produced by the placenta in the mother’s blood. From these data, the probability of a chromosomal change of the baby can be derived.
If abnormalities arise here, invasive procedures such as chorionic villus sampling or a somewhat later amniocentesis may be considered for clarification.
The statutory health insurance covers the costs of a chorionic villus biopsy; if there is a medical need for it, otherwise the parents have to pay the examination themselves.
The first-trimester screening is basically not part of the standard benefits of the health insurance companies. Including further investigations and advice, the total cost is between 100 and 200 euros.
It is recommended that both first-trimester screening and chorionic villus sampling be performed in a prenatal diagnostic center. The attending gynecologist will not perceive this step as a breach of trust, but on the contrary, mostly recommend it himself.
An open word
In any case, the parents should be advised in detail before each measure of prenatal diagnosis and also reflect the consequences of it for themselves. On the one hand, the invasive procedures are always associated with a – albeit minor – risk to the mother and child.
On the other hand, chromosomal changes cannot be treated. If a genetic injury to the baby is diagnosed, parents need to be clear about whether they have the opportunity to adopt their child as is or whether, for very different reasons, only abortion can be considered.
- Chorionic villus sampling is an invasive method of prenatal diagnosis, usually performed between the 11th and 14th week of gestation.
- The cells of the chorionic villi are placental cells – their genetic information is usually identical to the chromosome structure of the child’s cells.
- The test can, therefore, provide information about chromosomal changes and possible genetic damage to the baby at a relatively early stage of pregnancy.
- The risk of miscarriage due to chorionic villus sampling is between 0.5 and one percent.