PGD is an abbreviation for preimplantation genetic diagnosis. It is also known as PGT-M, from "monogenic" diseases study.

This technique is applied during in-vitro fertilization processes to ensure that the chosen embryos have not received a specific allele, genetic defect or mutation presented in their parents. After this genetic study, the embryos which are non-carriers of the alteration are selected, and transferred to a mothers' womb.

PGS is an abbreviation for preimplantation genetic screening. It is also known as PGT-A, from "aneuploidy" diseases study, and includes the determination of the chromosomal status of IVF embryos by screening all 23 pairs of human chromosomes.

This technique is also applied during in-vitro fertilization processes. Embryos could be carriers of different chromosomic alterations, produced during gamete development. The presence of aneuploidies in embryos is common, and their numbers increase with parental age.

Embryos with aneuploidies cannot implant and/or are the cause of fetal miscarriage.

However, with PGT-A is possible to detect the embryos with chromosomal alterations and discard them. Only euploid embryos will be transferred, increasing the chances of pregnancy. Unlike PGT-M, the PGT-A technique can be applied to all patients, especially those with advanced maternal or paternal age, with previous repeated miscarriages, etc.

These techniques have some limitations that should be exposed in their respective Informed consent forms.