Preimplantation Genetic Screening (PGS)
Preimplantation Genetic Screening (PGS) is a generalized test in which IVF embryos are screened for general chromosome number abnormalities (or aneuploidy.) Abnormalities in chromosome number can lead to failed IVF cycles, miscarriages, and/or birth defects. Many people use the terms PGS and PGD interchangeably, but PGD screens for known specific diseases and PGS does not.
PGS greatly reduces the possibility of discovering a serious genetic abnormality like trisomy 13, 18, or 21during pregnancy and subsequently facing the heart-wrenching decision of whether or not to carry the pregnancy to term.
When is PGS Indicated?
PGS testing is indicated when certain risk factors are present, including but not limited to:
- When the woman is 35 years of age or older
- When there is a history of miscarriages
- When the woman has experienced previously failed fertility treatments
Because chromosomal abnormalities are the leading cause of miscarriage, we commonly recommend PGS for couples who have had previous unsuccessful IVF cycles or who have experienced recurrent miscarriages in order to help improve their chances of a healthy pregnancy.
Couples already undergoing PGS to screen for chromosomal abnormalities will be able to know the gender chromosome allowing to select the gender of the embryo transferred, if family balancing is a secondary concern.
The PGS Procedure
The PGS process begins with egg retrieval and embryo culture as part of IVF. Once the retrieved egg has been fertilized in our laboratory, the embryo is allowed to develop for five days, at which time we biopsy three or four cells from what is now the trophectoderm, a layer of cells that will eventually become your baby’s placenta.
Under a high-power microscope and with the use of sophisticated, hydraulically-operated, ultrafine microscopic glass instruments, the Fertility Institute’s experienced embryology team stabilizes the embryo and makes a small hole in the shell surrounding the embryo.
This state-of-the-art technique, called “assisted hatching,” involves using a special laser to assist the embryo’s natural hatching process, creating a small window through which the cells emerge.
The small sample is then quickly microsurgically shaved off without significantly affecting the embryo and sent off for analysis.
The embryo is then frozen using vitrification, an ultra-rapid and safe freezing technique, and is paused in its development while the PGS testing takes place. When the results are received (usually in 7-10 business days), they will be discussed with the patient, and a frozen embryo transfer (FET) is scheduled. During the FET cycle, only a normal embryo or embryos are transferred into the woman’s uterus.
Preimplantation Genetic Diagnosis (PGD) vs. Preimplantation Genetic Screening (PGS)
We are often asked about the difference between PGD and PGS.
Basically, PGD is most commonly used when a couple is looking to diagnose or screen for a specific genetic disease, such as when the parents are carriers of Tay-Sachs disease, cystic fibrosis, or another single-gene mutation.
PGS, on the other hand, is a more generalized test in which the embryo is screened not for a specific genetic disease but rather for general chromosome number abnormalities (or aneuploidy.) Abnormalities in chromosome number can lead to failed IVF cycles, miscarriages, and/or birth defects. Many people use PGS and PGD interchangeably.