Cvs (Chorionic Villus Sampling)

Chorionic villus sampling (cvs), sometimes called "chorionic villous sampling" (as "villous" is the adjectival form of the word "villus"), is a form of prenatal diagnosis to determine chromosomal or genetic disorders in 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, earlier than amniocentesis or percutaneous umbilical cord blood sampling. It is the preferred technique before 15 weeks.

Possible reasons for having a cvs can include:
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.Screening Tests are usually carried out first before deciding if cvs should be done.