PGS: What Is Preimplantation Genetic Screening?

A woman's eggs are often chromosomally abnormal, and the percentage of eggs with a chromosomal abnormality increases with increasing female age. Many women who use in vitro fertilization (IVF) are older in maternal age (35 plus), which places them at increased risk for conceiving a child with chromosomal abnormalities.

Preimplantation genetic screening (PGS) is a process of screening embryos to make sure they have the right number of chromosomes and to look for any structural abnormalities in the chromosomes. The process is also called aneuploidy screening. This technique is thought to increase success rates for IVF in women over 35, as well as those who have suffered repeated IVF failure or recurrent miscarriage. However, this logic has not clearly been demonstrated with research.

With preimplantation genetic screening, one cell is removed from an eight-cell embryo created via IVF, and the eight chromosomes that malfunction most frequently are tested. Embryologists assess whether an embryo produced via IVF has chromosomal abnormalities in the cell. Chromosome abnormalities may include:

• Aneuploidy, which means the wrong number of chromosomes (a result of this could be Down Syndrome).
• Translocations, which means incorrect chromosome position.
• Other structural alterations that may be clinically significant.

PGS is done prior to the embryo transfer. Once the embryos have been tested, the couple can choose to transfer only embryos with the correct number of chromosomes into the womb. Embryos that have the normal number of chromosomes are more likely to result in a pregnancy that is carried to term.

Additionally, some fertility clinics allow patients to use PGS for gender selection.