Preimplantation Genetic Screening ( PGS )

PGS testing is a genetic study of the embryos produced during your IVF cycle which has a goal of helping you have a successful pregnancy and a healthy baby.

 PGS looks for aneuploidies, which is the presence of an abnormal number of chromosomes in an embryo, going forward, PGS Testing will be called Preimplantation Genetic Testing for Aneuploidies (PGT-A).

PGS testing screens your embryos for any chromosomal abnormalities before transferring the embryo into your uterus. If you and your doctor feel you could benefit from this test, it fits easily into your routine IVF treatment.

Who Should Consider It?

Overall, PGS helps to determine whether or not embryos appear to have the correct number of chromosomes. This is something many patients could benefit from, as it can increase pregnancy rates per transfer and reduce the risk of miscarriage, but it’s particularly recommended for the following:

  • If you’re over the age of 35 years old: The American College of Obstetricians and Gynecologists  have indicatedthat women over the age of 35 have a higher propensity for disorders that impair fertility and miscarriages. In addition, as women age, the chance for chromosomal abnormalities in embryos increases. PGS testing can be incredibly helpful for these patients by testing for chromosomal abnormalities in embryos prior to transfer.
  • If you’ve experienced more than two miscarriages: PGS testing is known to reduce miscarriage rates by testing for chromosomal abnormalities in embryos prior to transfer. This is because around half of all miscarriages are due to chromosomal abnormalities. In addition, you could speak with your doctor about  Products Of Conception (POC) testing, which is done on tissue from the lost pregnancy and evaluates the chromosomes to help provide insight into what has caused the miscarriage.
  • If you’ve had multiple rounds of IVF that were not successful: PGS testing is known to increase the likelihood of a successful embryo transfer by identifying which embryos appear chromosomally normal. In turn, this may help eliminate the need for as many cycles of IVF.

Ultimately, deciding if PGS testing is important or beneficial to your next IVF cycle is a conversation for you and your doctor to have. The ideal goal is for you to be well-informed about the options available to you so you can speak to your partner and reproductive endocrinologist about what you feel comfortable with and what will give you the best chance of a happy, healthy pregnancy.

What is PGS or preimplantation genetic screening?

PGS is used to determine whether the cells in an embryo contain the normal number of chromosomes, which is 46. After an embryo grows in the lab, it is usually biopsied on day 5 (blastocyst stage). A few embryo cells are then sent to an external lab which uses technology to count the number of chromosomes within each cell. Embryos with a normal number of chromosomes are “euploid” and those with an abnormal number are “aneuploid.” The purpose of PGS is to avoid transferring an abnormal embryo into the uterus.


Who benefits most from PGS?

All couples are at risk for having abnormal embryos. This risk increases significantly as a woman gets older. An abnormal embryo almost always fails to implant, or if it does, ends in a biochemical pregnancy (only hormone evidence of pregnancy), miscarriage, fetal death later in pregnancy, stillbirth or a baby with abnormalities.

Couples undergoing IVF may select PGS because they have severe male factor infertility, recurrent IVF failures, older age or a very large number of embryos. PGS can be used by those experiencing multiple miscarriages who may have different types of translocations where a piece of one chromosome breaks off and attaches to another chromosome resulting in a gain or loss of a cell’s genetic material.

Use of PGS has grown rapidly because of support by many physicians and patients who want to transfer a normal embryo. Some estimates suggest PGS is used in nearly 35 percent of all IVF cases and predict it may soon be used in half of all cycles.

Preimplantation genetic screening, or PGS, involves testing whether an embryo has the correct number of chromosomes before transferring it back to a woman’s uterus. This allows us to help determine which embryos have the best chance of becoming a healthy baby.

PGS Process

Five or six days after egg retrieval, at the blastocyst stage, a few cells are removed from the embryo. The cells are removed from the area of the embryo called the trophectoderm; these cells are destined to become the placenta, not the fetus. By avoiding transferring genetically abnormal embryos, this procedure reduces the chance of miscarriage, or when done to identify specific genetic disorders, may prevent the need for termination of pregnancy or the birth of a baby with a serious genetic disease. When genetic testing is performed to determine whether an embryo carries a specific disease-causing mutation it is called Preimplantation Genetic Diagnosis (PGD). Reproductive Partners Fertility Center – San Diego (RPSD) delivered the first PGD baby in San Diego County in 2001.

Improvements in Technique

The techniques for PGS have improved greatly over the past several years. Studies have found that biopsy of the embryo at the blastocyst stage does not negatively impact the embryo’s ability to implant into the uterus. In previous years when embryo biopsy was performed on the third day after fertilization there did appear to be a negative impact on the embryo’s ability to implant, and biopsy at this earlier embryo stage was more prone to error. Furthermore, technology now allows us to perform comprehensive chromosomal screening (checking all the chromosomes).  Thus, our current method of blastocyst biopsy is highly accurate and does not appear to pose significant risk to the embryo.By avoiding futile transfers where the embryo is destined to fail to implant or to miscarry, the birth rate per transfer is markedly increased.

Why PGS?

PGS is often recommended for women over 35 years old. As maternal age advances, a higher proportion of embryos are genetically abnormal. This higher prevalence of genetically abnormal embryos is the primary contributor to the decreased chance of successful pregnancy and increased chance of miscarriage in older women.

PGS may be considered when both partners are carriers for a specific genetic disorder, such as Cystic Fibrosis (CF). With CF, PGD is performed because one fourth of the embryos would carry both abnormal genes and be affected with this serious disease. With some other genetic diseases, half of the embryos will be abnormal. Also, patients may have an increased risk for miscarriage because one of the partners carries a genetic rearrangement in their chromosomes (translocation carrier), and genetic testing of embryos for these couples may reduce the risk of miscarriage.

Elective Single Embryo Transfer

PGS can also help us electively transfer a single genetically normal embryo, even for older women, and still offer couples an outstanding chance of success. By transferring only a single embryo, we can help avoid a twin pregnancy, which has much higher risks of complications for both mothers and babies. Studies have shown that electively transferring a single genetically normal embryo can increase the chance of having a healthy baby.