Chorionic villus sampling can be used during pregnancy to examine the unborn child for possible genetic disorders. It is possible to perform this examination method at a very early stage in pregnancy.
What is chorionic villus sampling?
Chorionic villus sampling can be used during pregnancy to examine the unborn child for possible genetic disorders. Prenatal diagnosis using chorionic villi was first described in 1983. It is an invasive examination method that can be used to detect chromosomal abnormalities and identify certain metabolic disorders. Chorionic villus sampling is recommended in cases of abnormalities in ultrasound, the presence of chromosomal abnormalities in the parents, or suspicion of certain inherited diseases. However, it is not a routine examination. Chorionic villus sampling is performed only after appropriate education and with the consent of the pregnant woman. If there is a suspicion or risk of disease in the unborn child, the health insurance company covers the cost of the examination. At the request of the parents, the chorionic villus sampling can also be performed in other cases at their own expense. However, a risk-benefit assessment should be made before the procedure. For example, an increased probability of trisomy 21 in the child is present in pregnant women aged 35 years and older and justifies diagnosis by chorionic villus sampling.
Function, effect, and goals of chorionic villus sampling.
Chorionic villus sampling can be used as a diagnostic method as early as the first trimester of pregnancy. From the eighth week of pregnancy, it is possible to analyze the cells from the so-called chorion. The method enables examination of the child’s chromosomes at the earliest possible stage during pregnancy, when other examinations such as amniocentesis are not yet possible. In the past, doctors used chorionic villus sampling as early as the ninth week of pregnancy. However, chorionic villus sampling should not be performed before the completed eleventh week of pregnancy and is now usually not performed at an earlier time. The chorion is a layer of cells on the outside of the amniotic sac. This layer of cells is evenly covered with villi, protrusions on the surface. Even though this is not cell material of the unborn child, it is genetically identical to the unborn child and is therefore suitable for diagnostics. The chorionic villi form part of the placenta, which supplies the unborn child with nutrients and oxygen. During chorionic villus sampling, chorionic villi are removed from the womb. This is done either with the help of a hollow needle, which the doctor inserts under ultrasound control through the abdominal wall into the placenta, and there cell material is taken by puncture. Another option is to collect chorionic villi through a catheter that passes through the vagina via the cervix into the placenta. Collection via the cervix is now rarely done because of higher risks. In some cases, however, chorionic villus sampling is not possible for anatomical reasons. For the subsequent genetic examination in the laboratory, 20 to 30 milligrams of chorionic villi are required. A chromosome image, known as a karyogram, is created from the extracted cells. In special cases, a DNA analysis can also be performed after prior genetic counseling. This allows the unborn child to be examined for molecular genetic diseases, such as various muscle diseases. With the help of the karyogram, various genetic peculiarities can be detected. These include trisomy 21, known as Down syndrome, trisomy 13 or Pätau syndrome, trisomy 18 or Edwards syndrome and trisomy 8. Some metabolic disorders can also be analyzed using the karyogram. The first results of the laboratory examination are available after only a few days. In the case of unclear findings, a long-term culture of the sampled cells is required, the results of which are available after approximately two weeks. Chorionic villus sampling is only performed at specialized centers and can therefore usually not be performed by a gynecologist in private practice.The aim of the examination is to detect or exclude genetic disorders at the earliest possible stage in pregnancy in order to avoid medical risks and psychological stress caused by a late termination of pregnancy. Parents should be informed in advance of a chorionic villus sampling about the lack of therapeutic options for curing most of the diseases that can be detected via this examination. If a genetic disease is detected, the only option is usually to adopt the child with the disease or terminate the pregnancy.
Risks, side effects, and dangers
Chorionic villus sampling increases the risk of miscarriage. Therefore, this examination method is chosen mainly when the risk of miscarriage is lower than the likelihood of chromosomal abnormality or the presence of a hereditary disease. There is also a low risk from the procedure of malformation of the child’s extremities. Vascular injury or bleeding, as well as infection, can also occur in rare cases after chorionic villus sampling. In rare cases, which are about two percent, misdiagnosis may occur. For example, the chorionic villi may be genetically different from the cells of the child. Similarly, in rare cases, cells within the placenta may be genetically different from each other. This is referred to as placental mosaicism. Examined cells may thus show a trisomy, although the unborn child has a normal set of chromosomes. Similarly, a trisomy may remain undetected during the examination. In the case of positive findings, it is sometimes recommended to confirm the examination result with a further examination, such as an amniocentesis. Meanwhile, the result of a fine ultrasound in the 13th week of pregnancy is often awaited before a chorionic villus sampling. Depending on the findings and the assessment of the risk for trisomy, a decision can then be made about whether to perform a chorionic villus sampling.
