chorionic villus sampling

chorionic villus sampling

chorionic villus sampling (CVS) or chorionic villus biopsy (CVB), diagnostic procedure in which a sample of chorionic villi from the developing placenta is removed from the uterus of a pregnant woman (see pregnancy) using a fine needle inserted through the abdomen or a thin plastic catheter inserted into the vagina and through the cervix. Chorionic villi are fingerlike projections of a membrane (the chorion) that surrounds the fetus. The villi develop from the fertilized ovum, or egg, and have a genetic composition similar to that of the fetus. Cells in the sample are grown in the laboratory and studied to detect the presence in the fetus of such genetic birth defects as Tay-Sachs disease and Down syndrome. The sex of the child can also be ascertained. Although CVS tests for the same range of abnormalities as amniocentesis, it is usually performed some weeks earlier (between the 8th and 12th weeks of pregnancy), and the results are available in a few days. It is recommended if the parents are carriers of certain genetic diseases, if there is a family history of genetic disorders, or if the woman is over age 35 (later pregnancies carrying with them a higher risk of chromosomal abnormality).
Chorionic villus sampling (CVS) is a form of prenatal diagnosis to determine chromosomal or genetic disorders in the fetus. It entails getting a sample of the chorionic villus ( placental tissue) and testing it. The advantage of CVS is that it can be carried out 10-13 weeks after the last period, earlier than amniocentesis (which is carried out at 15-18 weeks).


Possible reasons for having a CVS can include:


CVS is similar to amniocentesis in terms of fetal mortality (0.2 to 0.3%). Apart from a risk of miscarriage, there is a risk of infection and amniotic fluid leakage. The resulting amniotic fluid leak can develop into a condition known as oligohydramnios which is low amniotic fluid level. If the resulting oligohydramnios is not treated and the amniotic fluid continues to leak it can result in the baby developing hypoplastic lungs (underdeveloped lungs).

It is important after having a CVS that the OB/GYN follow the patient closely to ensure the patient does not develop infection.


A small percentage (1-2%) of pregnancies will have confined placental mosaicism, where some but not all of the placental cells tested in the CVS will be abnormal, even though the pregnancy is unaffected. Cells from the mother can be mixed in with the placental cells obtained from the CVS procedure. Occasionally if these maternal cells are not completely separated from the placental sample, this can lead to discrepancies with the results. This phenomenon is called Maternal Cell Contamination (MCC). CVS can not detect all birth defects. Only chromosomal abnormalities are usually tested for, or other specific genetic disorders if there is family history or other reason to test.

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