Pre-implantation genetic testing (PGT)

Pre-implantation genetic testing (PGT) is a screening test that can be done through the use of in vitro fertilization (IVF) where the embryos that are created can be tested for extra or missing chromosomes.

When to consider pre-implementation genetic testing?

Your embryos can be tested for abnormal chromosomes before they are transferred.  This is called preimplantation genetic testing, or PGT. It is done in a lab, using in vitro fertilization (IVF). One or more cells from each embryo is sent for genetic testing and you are able to work with a genetic councillor to understand the results.


You may want to consider PGT:



  • if you have experienced previous pregnancy loss

  • You are aged 35 or above

  • You have a family history of genetic disease or are carriers of a genetic mutation.


Please consult with your Fertility Specialist about what PGT options are best for you.

What is pre-implantation genetic testing for aneuploidy (PGT-A). Previously know as pre-implantation genetic screening or (PGS)?

Watch this video for more information on pre-implantation genetic screening (PGS)


Chromosomes are string-like structures found in the centre (nucleus) of cells. A human cell typically has 46 chromosomes. An embryo receives 23 chromosomes from the sperm and 23 from the egg. Chromosomes are important because they contain the information that instructs the body’s cells how to function. Chromosomal aneuploidy in an embryo can result in failure of an embryo to implant, pregnancy loss or the birth of a child with a chromosome abnormality like Down syndrome.


The goal of PGT-A is to identify embryos with aneuploidy and choose to transfer an embryo that has the correct number of chromosomes. This generally gives you a higher chance that the specific embryo will implant in your uterus.


When to consider PGT-A testing?


You might want to consider PGT-A if you are undergoing IVF, especially if you are 35 years old or above as aneuploidy risk increases with age, or if you have had previous pregnancy losses.


PGT-A may help reduce your chance of miscarriage or abnormal pregnancy. It may also reduce the time and cost you experience trying to have a healthy baby, by helping to select the best embryo for transfer. PGT-A can help reduce the risks associated with transferring multiple embryos at once.


PGT-A, like all screening tests, is not 100% accurate. It cannot guarantee you’ll have a chromosomally normal baby. It does not replace the prenatal screening that will be offered to you and all pregnant people. Also keep in mind that most birth defects are not related to missing or extra chromosomes, and some defects are not detectable before implantation or during pregnancy.

What is pre-implantation genetic testing for a monogenic disease (PGT-M)?

When people have a family history of a genetic disease or are carriers of a genetic mutation (often referred to as a single/monogenic gene disorder), they can consider undergoing pre-implantation genetic testing (PGT-M). This testing is done through the use of in vitro fertilization (IVF) where the embryos that are created can be tested for the specific genetic changes. The aim of PGT-M is to provide patients at risk of passing on a genetic disorder the opportunity to have a pregnancy that is unaffected by the disorder. 


When to consider PGT-M testing?


You might want to consider PGT-M if you would like to prevent passing on a specific genetic disease to your child. This includes X-linked, autosomal recessive and autosomal dominant diseases.


What are X-linked diseases?


We normally have 46 chromosomes in every cell. Chromosomes are the structures on which our DNA, our genes, are stored. An embryo receives 23 chromosomes from the sperm and 23 from the egg. Twenty-two of those are matching pairs called the autosomes. The twenty-third pair are the sex chromosomes and they are most commonly either XX or XY.  X-linked disorders are caused when there is a mutation in a gene on the X chromosome. Examples of X-linked disorders include hemophilia and Duchenne muscular dystrophy.


What are autosomal diseases?


Autosomal diseases are when there is a mutation in a gene on one of the autosomes.


Autosomal dominant diseases are genetic conditions that can occur if only one copy of the gene has a mutation. In cases of autosomal dominant diseases, one parent carries the abnormal gene, and the embryo has a 50% chance of being affected. Examples of autosomal dominant diseases include Marfan syndrome and neurofibromatosis type 1. 


Autosomal recessive diseases are genetic conditions that can occur only when an both copies of a gene have a mutation. When an individual has one copy of the gene with a mutation and one without, they are said to be carriers. Typically, being a carrier of a genetic condition does not have an impact on one’s health. When both parents are carriers for the same autosomal recessive disease, the embryo has a 25% chance of being affected. Examples of autosomal recessive diseases include cystic fibrosis and sickle cell anemia.


PGT-M is not 100% accurate. It cannot guarantee you will have an unaffected baby. Because it is not a perfect test, we strongly recommend that all people who get pregnant after doing PGT-M speak with a genetic counsellor about the risks and benefits of amniocentesis.

What is pre-implantation testing for structural rearrangements (PGT-SR)?

When people are carriers of a chromosomal translocation, they can consider undergoing pre-implantation genetic testing (PGT-SR). This testing is done through the use of in vitro fertilization (IVF) where the embryos that are created can be tested to determine if they contain the correct amount of genetic information. The aim of PGT-SR is to provide patients with known chromosomal rearrangements the opportunity to decrease the chances of experiencing a miscarriage and reduce the time it takes to achieve a healthy pregnancy. 


When to consider PGT-SR?


PGT-SR stands for preimplantation genetic testing of structural rearrangements, also known as chromosome translocations. Individuals who are known carriers of a balanced chromosomal translocation may consider PGT-SR.

What are the steps involved with PGT?


If you are interested in IVF and PGT-A, PGT-M or PGT-SR, first talk about it with your primary care provider.  They can refer you to Mount Sinai Fertility. After meeting with your Fertility Specialist, you will be referred to meet with a genetic counsellor. They will make sure you are fully informed before making a decision to move forward with the testing. With PGT-M and PGT-SR we will work with the genetic testing laboratory (also called the reference lab) to ensure that the genetic change can be reliably detected. This process is called case acceptance or probe development and must happen before you begin your IVF cycle.


For you, the patient, the steps will be the same as the IVF process. The difference is what happens in the laboratory when your embryos reach the blastocyst stage:



  1. Biopsy:  When your embryos have reached what is called the blastocyst stage – 5 to 6 days after fertilization – an embryologist will biopsy each embryo. During the biopsy, cells are removed from the outer layer of the embryo. Your embryos will then be frozen.



  1. Shipment:  The biopsied cells from your embryos are then sent to a reference lab to be tested. Your embryos remain frozen at Mount Sinai Fertility.



  1. Analysis:  The reference lab will look at all the chromosomes from your embryos.



  1. Review:  The results of the testing will be sent to your genetic counsellor and doctor at Mount Sinai Fertility. You will then speak to your genetic counsellor, who will explain the results to you.



  1. Transfer:  After you have reviewed the results with the genetic counsellor and have a suitable embryo for transfer, you can call your Day 1 for a Frozen Embryo Transfer cycle.

Expanded Carrier Screening (ECS)

Carrier screening is genetic testing that looks at the variants (mutations) in a person’s DNA to help determine the risk of having a child with a genetic condition.  

What is Expanded Carrier Screening?

Carrier screening is genetic testing that looks at the variants (mutations) in a person’s DNA to help determine the risk of having a child with a genetic condition.  


The expanded carrier screen analyzes up to 400 genes (out of our known 25,000 genes) to identify if you are a carrier of a genetic condition that could, otherwise unknowingly, be passed to your child. 


Most of us are carriers for many genetic conditions. Being a carrier means having one copy of a gene with a mutation and one without a mutation. Typically, we do not know what conditions we are carriers for, because carriers are typically healthy and do not show signs or symptoms of the condition. 


These conditions can be passed on in a family in two different ways: by autosomal recessive and X-linked recessive inheritance.


For most of our genes we have two copies — one we inherit from our fathers and one we inherit from our mothers. Autosomal recessive diseases are genetic conditions that can occur only when an both copies of a gene have a mutation. When an individual has one copy of the gene with a mutation and one without, they are said to be carriers. Typically, being a carrier of a genetic condition does not have an impact on one’s health. When both parents are carriers for the same autosomal recessive disease, the embryo has a 25% chance of being affected. Examples of autosomal recessive diseases include Cystic Fibrosis, Tay Sachs Disease, and Spinal Muscular Atrophy. 


X-linked Conditions are caused by disease-causing variants located on the X chromosome. Females typically have two X chromosomes while males typically have one X chromosome and one Y chromosome. Males that inherit disease-causing variants on the X chromosome are always affected, while females are often unaffected carriers. Examples of X-linked conditions include Duchene Muscular Dystrophy, Hemophilia, and Fragile X Syndrome.


The purpose of expanded carrier screening is to provide you with more information regarding the chance of having a child with a genetic condition. If an increased risk is identified, options for reducing this risk will be discussed with you and your partner.

When to consider Expanded Carrier Screening?

Couples who are concerned regarding the risk of having a child with a genetic condition may wish to consider expanded carrier screening to learn more about this risk.  All couples can consider this testing, regardless of their fertility status.

What are the steps involved with Expanded Carrier Screening?

If you are interested in expanded carrier screening, talk about it with your physician. If you are a patient at Mount Sinai Fertility, your fertility specialist can refer you to speak with a genetic counsellor. They will make sure you are fully informed before making a decision to move forward with the testing. In your conversation with the genetic counsellor, they will provide you with more information about this testing including possible outcomes, benefits and limitations, and options for testing and reporting. 


If you decide to move forward with testing, then the following process will occur:


Sample Collection:  We will help coordinate the collection of DNA through a cheek swab, saliva sample or blood draw. 


Shipment: The sample will then be shipped to the genetic testing laboratory.


Analysis:  Once the genetic testing laboratory receives the sample, they will analyze the sample and create a report


Review:  Your genetic counsellor will contact you when the report becomes available and review the results with you


Follow-up:  Your genetic counsellor will provide you with a copy of the report and coordinate any follow up appointments you may need.  


You may contact Mount Sinai Fertility Genetic Team at [email protected] for further information.