Chorionic villus sampling
Encyclopedia
Chorionic villus sampling (CVS), sometimes misspelled "chorionic villous sampling", is a form of prenatal diagnosis
to determine chromosomal or genetic disorders in the fetus
. It entails sampling
of the chorionic villus (placenta
l tissue) and testing it. CVS usually takes place 10–12 weeks after the last period, earlier than amniocentesis
(which is carried out as early as 14–16 weeks). It is the preferred technique before 15 weeks.
CVS was tested for the first time by Italian biologist Giuseppe Simoni
, scientific director of Biocell Center
, in 1983.
Use as early as 8 weeks in special circumstances has been described.
It can be performed in a transcervical or transabdominal manner.
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).
Additionally, there is also mild risk of Limb Reduction Defects associated with CVS, especially if the procedure is carried out in earlier terms (before 12th week of pregnancy).
It is important after having CVS that the OB/GYN follow the patient closely to ensure the patient does not develop infection.
, where some but not all of the placenta
l cells tested in the CVS are abnormal, even though the pregnancy is unaffected. Cells from the mother can be mixed with the placenta
l cells obtained from the CVS procedure. Occasionally if these maternal cells are not completely separated from the placenta
l sample, this can lead to discrepancies with the results. This phenomenon is called Maternal Cell Contamination (MCC). CVS cannot detect all birth defects. It is used for testing chromosomal abnormalities or other specific genetic disorders only if there is family history or other reason to test.
Prenatal diagnosis
Prenatal diagnosis or prenatal screening is testing for diseases or conditions in a fetus or embryo before it is born. The aim is to detect birth defects such as neural tube defects, Down syndrome, chromosome abnormalities, genetic diseases and other conditions, such as spina bifida, cleft palate,...
to determine chromosomal or genetic disorders in the fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
. It entails sampling
Sampling (medicine)
In medicine, sampling is gathering of matter from the body to aid in the process of a medical diagnosis and/or evaluation of an indication for treatment, further medical tests or other procedures...
of the chorionic villus (placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l tissue) and testing it. CVS usually takes place 10–12 weeks after the last period, earlier than amniocentesis
Amniocentesis
Amniocentesis is a medical procedure used in prenatal diagnosis of chromosomal abnormalities and fetal infections, in which a small amount of amniotic fluid, which contains fetal tissues, is sampled from the amnion or amniotic sac surrounding a developing fetus, and the fetal DNA is examined for...
(which is carried out as early as 14–16 weeks). It is the preferred technique before 15 weeks.
CVS was tested for the first time by Italian biologist Giuseppe Simoni
Giuseppe Simoni
Giuseppe Simoni is an Italian biologist and scientist. He was born in Pavia, Italy in 1944, and obtained his degree in biology at the University of Milan, where he later became a professor of genetics and biology for thirteen years....
, scientific director of Biocell Center
Biocell Center
Biocell Center is an international company specializing in the cryopreservation and private banking of amniotic fluid stem cells. The company is headquartered in Italy with several international locations and is involved with numerous partnerships and research studies of amniotic fluid stem...
, in 1983.
Use as early as 8 weeks in special circumstances has been described.
It can be performed in a transcervical or transabdominal manner.
Indications
Possible reasons for having a CVS can include:- Abnormal first trimester screen results
- Increased nuchal translucency or other abnormal ultrasoundObstetric ultrasonographyObstetric sonography is the application of medical ultrasonography to obstetrics, in which sonography is used to visualize the embryo or foetus in its mother's uterus...
findings - Family history of a chromosomal abnormality or other genetic disorderGenetic disorderA genetic disorder is an illness caused by abnormalities in genes or chromosomes, especially a condition that is present from before birth. Most genetic disorders are quite rare and affect one person in every several thousands or millions....
- Parents are known carriers for a genetic disorder
- Previously, maternal age above 35 has been an indication for CVS. Note that maternal age alone is now rarely a reason to undergo diagnostic test like CVS, given its higher risk. High maternal age is associated with increase risk of Down's syndrome and at age 35, risk is 1:400. Screening test are usually carried out first before deciding if CVS should be done.
Risks
Risk of miscarriage in CVS in about 0.5 - 1%. Apart from a risk of miscarriage, there is a risk of infection and amniotic fluidAmniotic fluid
Amniotic fluid or liquor amnii is the nourishing and protecting liquid contained by the amniotic sac of a pregnant woman.- Development of amniotic fluid :...
leakage. The resulting amniotic fluid leak can develop into a condition known as oligohydramnios
Oligohydramnios
Oligohydramnios is a condition in pregnancy characterized by a deficiency of amniotic fluid. It is the opposite of polyhydramnios.-Diagnosis:Diagnosis is made by ultrasound measurement of the amniotic fluid index...
, which is low amniotic fluid level. If the resulting oligohydramnios
Oligohydramnios
Oligohydramnios is a condition in pregnancy characterized by a deficiency of amniotic fluid. It is the opposite of polyhydramnios.-Diagnosis:Diagnosis is made by ultrasound measurement of the amniotic fluid index...
is not treated and the amniotic fluid continues to leak it can result in the baby developing hypoplastic lungs (underdeveloped lungs).
Additionally, there is also mild risk of Limb Reduction Defects associated with CVS, especially if the procedure is carried out in earlier terms (before 12th week of pregnancy).
It is important after having CVS that the OB/GYN follow the patient closely to ensure the patient does not develop infection.
Limitations
A small percentage (1-2%) of pregnancies have confined placental mosaicismConfined placental mosaicism
Confined placental mosaicism represents a discrepancy between the chromosomal makeup of the cells in the placenta and the cells in the baby. CPM was first described by Kalousek and Dill in 1983...
, where some but not all of the placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l cells tested in the CVS are abnormal, even though the pregnancy is unaffected. Cells from the mother can be mixed with the placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l cells obtained from the CVS procedure. Occasionally if these maternal cells are not completely separated from the placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l sample, this can lead to discrepancies with the results. This phenomenon is called Maternal Cell Contamination (MCC). CVS cannot detect all birth defects. It is used for testing chromosomal abnormalities or other specific genetic disorders only if there is family history or other reason to test.
See also
- AmniocentesisAmniocentesisAmniocentesis is a medical procedure used in prenatal diagnosis of chromosomal abnormalities and fetal infections, in which a small amount of amniotic fluid, which contains fetal tissues, is sampled from the amnion or amniotic sac surrounding a developing fetus, and the fetal DNA is examined for...
- Percutaneous umbilical cord blood samplingPercutaneous umbilical cord blood samplingPercutaneous umbilical cord blood sampling , also called cordocentesis, is a diagnostic genetic test that examines blood from the fetal umbilical cord to detect fetal abnormalities. PUBS provides a means of rapid chromosome analysis and is useful when information cannot be obtained through...
- Prenatal diagnosisPrenatal diagnosisPrenatal diagnosis or prenatal screening is testing for diseases or conditions in a fetus or embryo before it is born. The aim is to detect birth defects such as neural tube defects, Down syndrome, chromosome abnormalities, genetic diseases and other conditions, such as spina bifida, cleft palate,...
External links
- March of Dimes
- Cleveland Clinic
- CVS Test: Six Months of Worry Free Pregnancy
- Chorionic Villus Sampling - slideshow by The New York TimesThe New York TimesThe New York Times is an American daily newspaper founded and continuously published in New York City since 1851. The New York Times has won 106 Pulitzer Prizes, the most of any news organization...