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The IVF Fertility Blog

What is PGD/PGS and what is the difference?

who needs pgd/pgs/ngs and what are the applications?

Following my last video, today I would like to discuss what is PGS (preimplantation genetic screening) and what is PGD (preimplantation genetic diagnosis) and what are the applications and who needs it.


We know that we are all made of cells and that each cell contains a nucleus which holds the DNA.  DNA has all the information about what makes us, us.  Who we are, are we healthy, and how we develop.  If DNA gets messed up in conception then it could result in miscarriage, no pregnancy, still births, and other issues.   The same thing goes for DNA inside embryos and their chromosomes.  If there are chromosomal abnormalities, then there could be birth complications, not implanted, miscarriage, abnormal baby at birth, like Downs syndrome.

Recent technology allows us to take the cell through a special embryo biopsy technique, and allow us to do genetic testing on the cells (more accurately gene testing) to determine if anything is abnormal.  The newest of these techniques is called NGS (next generation sequencing) to check the DNA.  Using various techniques we can detect all the different problems within developing embryos.

So what is the difference between PGD and PGS? 


Well, generally speaking there isn’t that great of a difference.  If we are doing both tests to diagnose genetic disease, say a couple that we know carries a genetic disease, we will use PGD to diagnose whether or not this gene has been passed onto the embryo.  For example, both parents may be carriers for Cystic Fibrosis, a recessive disease, which means there is a 1/3 likelihood that their baby will have it, and we can diagnose it using PGD. 

PGS will be used to screen out abnormalities that may exist in anyone but aren’t specifically known to exist and thus aren’t easily predictable through one of the parent’s genetic dispositions.  This is more commonly used in a patient who is trying to get pregnant and who might have age-related issues or age-related miscarriages.  For example, a woman who is 39-years old will have a 30% chance of miscarriage due to chromosomal abnormality.  But we can screen out these problems and increase the chance of pregnancy. 


So again the difference between PGS and PGD is that with PGD you already know there is a potential for abnormality  but with PGS we are unaware of any particular deficiency and so are screening for chromosomal age-related problems.  Most tests are PGS.


In modern IVF approaches, and in our own practice, we recommend universally screening all embryos to ensure better implantation rate and lower rates of miscarriage.




Topics: PGD, Mini-IVF, IVF, genetic screening, pgs, miscarriage, ngs

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