<prompt> Chorionic villus sampling is generally performed between8 to 10 weeks10 to 13 weeks15 to 18 weeks20 to 24weeks  <response>: Biopsy of chorionic villi is generally performed between 10 and 13 weeks gestation. Although most procedures are performed to assess fetal karyotype, numerous specialized genetic tests can also be performed by chorionic villus sampling CVS. The primary advantage of villus biopsy is that results are available earlier in pregnancy, allowing safer pregnancy termination if desired. 