Pgs is a screening tool to look at the chromosomal content of the embryos whereas PGD is diagnostic where we look for a specific genetic abnormality/mutation. It is often confused but have very different purpose and meaning.

Many people, patients and clinicians included, can confuse PGD and PGS. These terms are often used interchangeably incorrectly. PGD stands for pre genetic diagnosis and PGS stands for pre genetic screening. When a couple does PGD they are testing for a specific genetic mutation (think cystic fibrosis or tay Sachs disease). However when a couple does PGS (which is what most people do) they are screening an embryo for chromosome number; not a specific genetic mutation.

Some additional info to that one that posted Dr Munne. Nowadays, there are several techniques to do PGS. The newest is NGS. This new technique allowed as to classify embryos as normal, abnormal and mosaicisms. It is very important to talk about the meaning of each of them before doing PGS, to better understand what to do when you receive the report. We do a lot of PGS with NGS and implantation rates are incredibly high, it doesn't matter the age of the woman.

PGD is the general term for the this diagnostic technology that includes testing embryos for genetic disorders before transferring them back to the uterus. PGS is only a part of PGD that deals with screening the embryos to reveal any numerical chromosomal abnormalities.