When is it done:
Usually between 9-14 weeks.
This test is usually offered to women who are considered high risk for having babies with genetic disorders such as cystic fibrosis or chromosomal abnormalities.
A sample of the cells that line the placenta, known as chorionic villi, are extracted either by using a fine needle which passes through the abdomen (transabdominal CVS) or via a catheter which is inserted through the cervix (transcervical CVS) into the placenta. The sample is then analysed. Because no amniotic fluid is retrieved during the procedure, CVS cannot detect neural tube disorders.
The results take about one to three weeks depending on the type of condition being detected. Although there is a risk of miscarriage when doing this test, it is estimated at only around 1%, provided the operator is as experienced in this technique as in amniocentesis.