Trophoblast sampling: light micrograph of human trophoblast tissue, removed from a pregnant woman for pre-natal diagnostic screening for congenital disorders such as Down's syndrome & thalassaemia. Trophoblast tissue forms the walls of the blastocyst, the hollow ball of cells that surrounds the early embryo. Trophoblast sampling can be performed as early as the 9th week of pregnancy, by suction through a flexible tube inserted via the cervix into the uterus. Cells removed in this way are subsequently examined for genetic abnormalities. Chorionic villus sampling (CVS) - a new procedure involves removing a small sample of the developing placenta on which to perform a range of genetic tests. (Chromosome analysis, DNA tests, enzyme analysis It can be performed much earlier in