Embryos created by IVF (In Vitro Fertilisation)can be tested for
some genetic disorders before embryo transfer takes place.
One or two blastomere (cells) are taken from
an embryo after cleavage has progressed to beyond the eight cell stage, or
(more recently) groups of cells are removed from the trophoblast cells of the
blastocyst stage - taking more cells improves the accuracy of the
procedure.
Those cells removed are analyzed using either polymerase chase reaction (PCR) procedures or fluorescence in situ hybridization (FISH) techniques after amplification of the genetic material. The procedure can be carried out in a matter of hours enabling decisions by the 'parents' as to which embryos should be transferred.
So far such procedures have been carried out to diagnose the sex of the fetus, aneuploidy (wrong chromosome numbers) Cystic fibrosis, Tay Sachs disease, Duchene muscular dystrophy, Lesch-Nyhan syndrome. As more gene marker become available other disorders may soon be diagnosed.
Some groups have questioned whether such procedures are ethically
acceptable particularly where sex selection was concerned. A recent report
suggested that it was in carefully defined circumstances:-
Using
preimplantation genetic diagnosis to determine the sex of an embryo conceived
by IVF is ethically acceptable, but only if the aim is to avoid the
transmission of genetic disorders, according to the ethics committee of the
American Society for Reproductive Medicine. This is the only reason for
choosing the sex of children that avoids the potential of "gender bias," the
panel says in the October issue of Fertility and Sterility. The panel's report
focuses on the use of preimplantation genetic diagnosis for sex selection.
Although the practice is rare, they note "...the increasing attractiveness of
pregnancy sex selection..." to some individuals compared with other methods of
sex selection, such as abortion. According to a press release from the American
Society for Reproductive Medicine, "this Ethics Committee Statement supports
the use of preimplantation genetic diagnosis and sex selection to prevent the
transmission of genetic diseases and discourages use of this technology for
nonmedical family balancing or family planning purposes." Fertil Steril
1999;72:595-598