In PGS or pre-implantation genetic screening we count the number of all chromosome pairs in one or several cells of the embryo. Embryos with an abnormal number of chromosomes are termed aneuploid, hence this technique is also called ‘screening for aneuploidy’. Aneuploid embryos are not returned to the uterus because they are not viable or can give rise to the birth of a child with problems.
Genetic embryo analysis and embryo transfer
Under PGD we have seen that there are two options in timing the embryo biopsy
and the embryo transfer
- In PGS we prefer to perform the genetic analysis on day five after fertilisation, because then we can examine several cells and thus more DNA.
- It is also possible that we perform a biopsy at day 3, with the same microarrays, and that we freeze the embryos at day 5 of development.
In short, in all cases the transfer back of the embryos with normal chromosomes is scheduled for a later, non-stimulated cycle – and after the genetics doctor has discussed the result of the screening with you.
Nevertheless, if only a limited number of embryos are available at day three of development, it may be possible – after discussing it with your doctor – not to perform genetic screening and simply return the available embryos to the uterus.