What are the different types of PGD testing?
In discussing PGD for gender selection, we usually assume that PGD just means determining the embryo's sex. But there are actually 3 different types of genetic testing that can be performed during PGD, and understanding these may improve your chances of a healthy pregnancy.
Determining whether the embryo is male or female is the simplest PGD test, because it's only necessary to check the last pair of chromosomes: XX is a girl, and XY is a boy.
Chromosome Abnormality (Aneupolidy)
PGD testing can also check to make sure the embryo has the correct number of chromosomes. Having the wrong number of chromosomes is called aneuploidy, and it means that there is either a missing chromosome, or an extra chromosome, instead of the normal 23 pairs.
Being able to screen out chromosomally embryos not only reduces the odds of having a baby with birth defects, but can drastically increase your chance of having an IVF cycle resulting in successful pregnancy.
Single Gene Disorders
For parents who are at risk of passing on inherited genetic disorders, PGD can be used to check the embryo for the disorder, and select only unaffected embryos. For example, if one of the parents has, or is a carrier of, cystic fibrosis (the most common genetic disorder in the US), embryos can be screened for CF and only embryos which do not have CF are selected. Further, embryos which are not CF carriers can be identified, so that the child does not pass CF on to its own offspring.
A long list of diseases which are caused by a single gene defect have been identified, and can be tested for with PGD. Even with very rare conditions, it is possible for the parents to undergo genetic testing and have a new PGD probe developed (at, of course, additional cost).