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.

[2] CVS was performed for the first time in Milan by Italian biologist Giuseppe Simoni, scientific director of Biocell Center, in 1983.

However some recent research has suggested that only a very small number of miscarriages that occur after CVS are a direct result of the procedure.

Occasionally if these maternal cells are not completely separated from the placental sample, this can lead to discrepancies with the results.