via the withdrawal of amniotic fluid from the uterus at 16 weeks gestation.2. cvs. chorionic villus sampling is used by extracting tissue from the chorion between 10 and 12 weeks gestation.3. pgd. preimplantation genetic testing is the testing of embryos prior to implantation by extracting one to two cells from the embyro. the embyro is not implanted if a genetic disorder is discovered.turner syndromea chromosomal disorder in females in which either an x chromosome is missing