Chorionic villus sampling, also known as chorionic villus biopsy, is an invasive procedure for prenatal diagnosis in which a sample of placental tissue (see placenta), containing chorionic villi, is aspirated through the cervix or abdomen under ultrasound visualization.

Chorionic villus sampling is usually performed between the 10th and 13th weeks of gestation. The cells so obtained are subject to chromosomal analysis to determine if any abnormalities are present in the fetus. This enables the diagnosis of chromosomal abnormalities such as Down's syndrome.