Chorionic villus sampling(CVS)
sometimes called "chorionic villous sampling" is a form of prenatal diagnosis to determine chromosomal or genetic disordersin the fetus.
It entails sampling of the chorionic villus (placental tissue) and testing it for chromosomal abnormalities, usually with FISH or PCR. CVS usually takes place at 10–12 weeks' gestation.
It can be performed in a transcervical or transabdominal manner.
Although this procedure is mostly associated with testing for Down Syndrome, overall, CVS can detect more than 200 disorders.
Indication
- Abnormal first trimester screen results
- Increased nuchal translucency or other abnormal ultrasound findings.
- Family history of a chromosomal abnormality or other genetic disorder.
- Parents are known carriers for a genetic disorder.
- Advanced maternal age (maternal age above 35). AMA is associated with increase risk of Down's syndrome and at age 35, risk is 1:400.
Risks
The risk of miscarriage in CVS is estimated to be about 1-2%.
Nuchal translucency
Nuchal translucency is a ultrasound (USG) finding during a specific period in the late first trimester and early second trimester (11.3-13.6 weeks).
Common associations
Thickening of the nuchal translucency can be associated with a number of anomalies, including:
Aneuploidy
- Trisomies (including Down syndrome)
- Turner syndrome
Non-aneuploidy structural defects and syndromes
- congenital diaphragmatic herniation
- congenital heart disease
Interpretation
The rate of aneuploidy when the nuchal translucency is < mm is less than 1%.
Correlation with serum markers
The combination of nuchal translucency thickness, PAPP-A, and hCG detects 87% of cases of trisomy 21 at 11 weeks, 85% at 12 weeks, and 82% at 13 weeks, with a 5% false positive rate.
Amniocentesis:
Amniocentesis is a prenatal test in which a small amount of amniotic fluid is removed from the sac surrounding the fetusfor testing. The fluid is then sent to a laboratory for analysis. Different tests can be performed on a sample of amniotic fluid, depending on the genetic risk and indication for the test.
- Abnormal first trimester screen results
- Increased nuchal translucency or other abnormal ultrasound findings
- Family history of a chromosomal abnormality or other genetic disorder
- Parents are known carriers for a genetic disorder
- Advanced maternal age (maternal age above 35). AMA is associated with increase risk of Down's syndrome and at age 35, risk is 1:400.
When Is Amniocentesis Performed?
The procedure is usually scheduled between the 15th and 18th week of pregnancy.
Does Amniocentesis Have Risks?
Yes. There is a small risk that an amniocentesis could cause a miscarriage (less than 1%, or approximately 1 in 200 to 1 in 400). Injury to the baby or mother, infection, and preterm labor are other potential complications that can occur, but are extremely rare.
Anomaly scan
This detailed ultrasound scan, sometimes called the mid-pregnancy or 20-week scan, is usually carried out when you are between 18 and 21 weeks pregnant. In some areas it may be carried out later than 21 weeks. The scan checks for major physical abnormalities in your baby, although it can't pick up every problem.
The mid-pregnancy anomaly scan looks for some physical abnormalities in the baby. Detailed study of the baby's bones, heart, brain, spinal cord, face, kidneys and abdomen.
Can the scan harm me or my baby?
There are no known risks to the baby or you from having an ultrasound scan.