Embryo biopsy

Embryo biopsy, or preimplantation diagnosis, is used to screen embryos for diseases that may be inherited from one or other parent, such as cystic fibrosis, hemophilia or Tay-Sachs. In the procedure a single cell is removed from the embryo two or three days after an egg has been fertilized. The remaining cells will continue to grow, as the procedure usually does no harm to the embryo. The cell removed is examined for genetic defects. The sex of the embryo can also be determined, as can chromosomal defects that lead to Down Syndrome.