Preimplantation Genetic Screening (PGS)

Last updated date: 17-Aug-2023

Originally Written in English

Preimplantation Genetic Screening (PGS)

Preimplantation genetic screening (PGS) can also be referred to as embryo biopsy. It refers to procedures that detect genetic or chromosomal abnormalities in embryos before their use in IVF. PGS screens for a wide variety of genetic issues or chromosome defects, impacting 25 to 28% of embryos based on a woman's age. Aside from their function in certain disorders, chromosome defects are associated with an increased risk of failed IVF and miscarriage. 

Medical providers usually conduct PSG tests to determine the normal embryos genetically. Genetic tests can reduce the likelihood of passing on a heritable, crippling disease to an infant. This is especially in couples who have a proven risk of such disorder. Genetic tests are also helpful in increasing the likelihood of a successful pregnancy. This is through screening for possible genetic conditions that can adversely impact conception, pregnancy, and delivery.


Why Preimplantation Screening is done 

Preimplantation Screening

PGS is widely applicable in evaluating embryos for the normal number of chromosomes through cell biopsy and examination. This process is referred to as euploidy. Usually, an embryo consists of 23 chromosomes. They are usually passed on by both parents through fertilization, making a total of 46 chromosomes. Aneuploidy is described as the abnormal number which is either too many or less. It is the major foundation of congenital disabilities as well as pregnancies. 

Some of the common health conditions that arise due to chromosome abnormalities are; 

  • Turner syndrome 
  • Down syndrome 
  • Klinefelter syndrome 

Individuals and partners should consider PGS if they are confirmed to have the chromosomal anomalies that cause the disorders mentioned above or if they are suspected of having them, which is usually decided by a quantitative family history review by a professional geneticist. PGS details can help couples and individuals have a baby free of congenital disabilities caused by chromosomal abnormalities. 

Other additional benefits of preimplantation genetic testing include the following; 

  • Reduce the likelihood of miscarriage 
  • Limit the possibility of an abnormal pregnancy 
  • Enhance the chances of having a successful birth 
  • Increase the odds of a successful pregnancy through the use of elective single embryo transfers (eSET). This eliminates the possibility of having multiples, twins, or more and the associated health complications in both the mother and baby. 
  • Decrease the amount of time and expenses associated with various cycles of IVF. 
  • Increase the likelihood of a healthy pregnancy in women aged 37 and over. This is because age raises the odds of chromosome defects in an embryo.


How Preimplantation Genetic Screening Works 

How does preimplantation genetic screening work? Generally, it involves taking a biopsy at the blastocyst level. This is normally reached on the 5th or 6th day of embryo development. Therefore, embryologists take four to six cells from the 100-200 cell blastocyst to conduct embryo biopsies. The biopsy is then brought to the lab for a preimplantation genetic screening examination. Embryos are usually frozen and stored at the fertility center as the biopsies are conducted in the laboratory. 

Preimplantation genetic screening examines every embryo biopsy and quantifies the chromosome number in every sample. Usually, the normal embryo consists of 46 chromosomes or a total of 23 pairs of chromosomes. One set is contributed by the semen source while the other by the egg source. The embryos that the physician identifies to be euploid or chromosomally normal have a much greater possibility of implantation. There are also increased chances of continuing pregnancy and producing a healthy infant, unlike the abnormal embryos. 

If any of the 46 chromosomes are deviant, the embryo is usually considered aneuploid or abnormal. Therefore, whenever the embryo is aneuploid, one or more chromosomes are absent or excess. An embryo having an absent or more chromosome is more likely to undergo implantation failure or miscarriage. It could also result in a pregnancy impaired by a chromosomal syndrome. 

After the analysis of every embryo, a genetic analysis will be sent to the reproductive endocrinologist. The doctor will then use the findings, along with the embryo grading or morphology, to make a decision on the embryo to transfer. 


Candidates for Preimplantation Genetic Screening 

The use of preimplantation genetic screening boosts the rates of success for frozen embryo transfers. While PGS involves an extra phase in the IVF method, screening can dramatically lessen the possibility of miscarriage and failed transfers.

It is also essential to note that the risk of chromosome abnormality rises with age in women. If you are above the age of 35, you can talk to your fertility specialist about preimplantation genetic screening. On the other hand, young women might still have a relatively higher chance of chromosomal errors in embryos.

Thus, PGS is suitable for all women regardless of age, especially those who experience a recurring miscarriage. This is irrespective of whether they conceived via fertility treatment procedure or naturally. 


The Commonly Performed Preimplantation Genetic Screening Tests 

Embryonic cells may be screened for a mutation that induces a particular disease. This will reveal whether an embryo is normal without any disease or abnormal and has the disease. It would also reveal whether the embryo carries the disease but is untouched by it. A non-affected carrier is a person who can transfer the disease on to his or her offspring but may not have any symptoms of the condition themselves.

Another kind of genetic test that can verify the chromosomes is a karyotype. During a pregnancy, either chorionic villus screening or amniocentesis is performed. This measure reveals whether the fetus has more or fewer chromosomes than the normal 46. Disorders caused by having too many or fewer chromosomes include Down syndrome (Trisomy 21) and Trisomy 13.

This test will also search for the out-of-order chromosomes, known as translocations, which can trigger growth or function issues. Per year, the range of genetic tests available gradually increases.


Advantages of Preimplantation Genetic Screening (PGS) 

Early pregnancy miscarriages are often caused by chromosomal defects, which account for about 70% of all miscarriages. As a result, the preimplantation genetic screening will improve the chances of having a healthy and successful pregnancy. 

Other additional advantages of preimplantation genetic screening include the following; 

  • Increased likelihood of a successful birth in all age ranges. 
  • High conception rates per embryo transfer
  • Reduced cycles of IVF procedures 
  • Enable single-embryo transfer through the selection of the embryo with the highest possibility of implanting and resulting in the birth of a healthy infant. Single Embryo Transfer (SET) can aid in reducing the risk of health problems related to twin or triplet pregnancies. Furthermore, multiple births can raise the risk of pregnancy complications, including preterm delivery, preeclampsia, and abnormal placenta function.
  • Preimplantation genetic screening will help you shorten the time between IVF periods. For instance, if you undergo an IVF cycle while the normal embryo is not found, you might automatically begin the next cycle.


Risks Associated With Preimplantation Genetic Testing (PGS)

Babies born after PGS testing face the same health threats as children born following a standard IVF procedure. Besides, they are a bit higher, unlike children born via traditional pregnancies. These dangers involve low birth weight and high possibilities of multiple births, which can be twins or more. 

Certain embryos can be altered or damaged during cell extraction for preimplantation genetic screening (PGS) examination. This chance is incredibly low, but it may lead to an embryo ceasing to develop. Otherwise, the health risks and effects of genetic tests are similar to those involved with IVF.

PGS includes ethical problems on which people can have deep views and beliefs. These problems impact partners in various ways. Hence, consulting with the specialist before undergoing PGS is highly essential. The most common concern is that a genetic defect or chromosomal anomaly in an embryo might never develop as a disorder in the child's life. On the contrary, deciding to discard the embryo is usually difficult.


What is Preimplantation Genetic Diagnosis (PGD)? 

Preimplantation Genetic Diagnosis

Most disorders are caused by particular gene defects in DNA, which embryologists can diagnose usingpreimplantation genetic diagnosis (PGD). People or couples who are identified carriers with a certain genetic disease or who have a family history of the condition are more likely to have a baby with the genetic condition. 

A person doesn't need to have the genetic disorder in order to pass it on to the infant. As a result, family history is a significant predictor of a possible genetic problem. A geneticist evaluates a couple's or individual's family background in order to find issues in their family tree. Hence, they can prescribe PGD as a result.



Preimplantation genetic screening assists in the selection of chromosomally normal and fit embryos for transfers. PGS increases transfer success rates and assists patients in achieving successful pregnancies and healthy babies. 

Therefore, as you plan for your IVF treatment procedure, consulting a physician about preimplantation genetic screening is essential. Through this, you will also know if they think it is a good fit for your fertility background and objectives. As stated above, PGS has medical advantages for you and your unborn children. This is because it screens and tests embryos for chromosomal disparity before being transferred to the uterus.