Preimplantation genetic testing (PGT)

Key Points

Preimplantation genetic testing assesses embryos developed through in vitro fertilization (IVF) to identify genetic conditions affecting the potential child’s health and viability before uterine implantation.
PGT is particularly valuable in conjunction with IVF, as genetic issues in the embryo are a significant cause of pregnancy failure. The test involves a biopsy of the embryo at the blastocyst stage, wherein a small number of cells are extracted from the outer layer of the embryo.

There are three types of PGT:

PGT-A (formerly known as PGS) examines the chromosomes’ number abnormalities (aneuploidy) that may lead to conditions like Down syndrome.
PGT-M (formerly known as PGD) assesses for single genetic disorders such as cystic fibrosis.
PGT-SR tests for disorders that alter the normal structure of chromosomes, often resulting in miscarriage.

Overview

What is Preimplantation Genetic Testing?

Preimplantation genetic testing (PGT) is a specialized genetic examination exclusively conducted on embryos generated through the in vitro fertilization (IVF) process. PGT assesses embryos in the laboratory for various genetic disorders before their implantation in the mother’s womb to ensure a healthy pregnancy. Given that multiple embryos are often created in the IVF context, PGT aids our embryologist in selecting embryos that are devoid of genetic issues.

These issues encompass single gene disorders that parents may transmit to their children and anomalies like aneuploidy, where embryos possess either too few or too many chromosomes in a pair. Additionally, PGT can identify instances where chromosome material in the DNA is disrupted due to rearrangement.

All the conditions can lead to pregnancy failure and pose risks of child death or disability. This holds true for both natural and IVF pregnancies, but PGT offers a means to test IVF embryos, minimizing the likelihood of such occurrences.

An alternative method for testing genetic abnormalities during pregnancy involves procedures like amniocentesis. This invasive test, performed after 15 weeks of pregnancy, uses a hollow needle to extract material from the fetus, which is then assessed for genetic issues like those addressed by PGT before pregnancy.

It’s important to distinguish PGT from preconception genetic testing or screening, which occurs before attempting pregnancy and involves evaluating the parents’ DNA for potential genetic conditions that could be inherited by their child.

Dr. Jovanovic, our fertility specialist with expertise in genetics, is available to provide preconception genetic counselling. Additionally, PFC can assist patients in arranging preconception genetic testing through external laboratories.

Procedure

PGT Embryo Biopsy

Our laboratory conducts the embryo biopsy procedure, which entails extracting a small number of cells from the trophectoderm of the blastocyst, the part that develops into the placenta. It’s important to note that cells destined to become the fetus are not utilized in this process.

Following the biopsy, we send the collected sample to an external laboratory for DNA testing. This lab employs advanced next-generation sequencing, combining computer power with molecular evaluation to provide the most accurate and precise information.

Our Approach

Recommending PGT

PFC provides our patients with Preimplantation Genetic Testing (PGT) in conjunction with time-lapse incubator technology, aiding in the detection of any potential issues during embryo development.

Individuals who may benefit from considering PGT include:

Women aged 35 or older, as advanced maternal age heightens the likelihood of genetic defects in embryos.
Couples or individuals with a history of recurrent miscarriage attributed to abnormal chromosomes.
Couples facing a known or suspected risk of transmitting inheritable genetic diseases.

PGT-A

Preimplantation Genetic Testing for Aneuploidy

Humans possess 23 pairs of chromosomes (one from each parent), totaling 46. When a sperm or egg cell undergoes improper division, it can result in an abnormal number of chromosomes, known as aneuploidy. PGT-A is designed to screen for this issue. The risk of aneuploidy rises with age, serving as a significant factor in implantation failure and miscarriage, whether through IVF or natural attempts to conceive. Additionally, aneuploidy is a leading cause of birth defects in children.

Monosomy, characterized by too few chromosomes, and trisomy, characterized by too many chromosomes, are the two outcomes of this irregular division. Nearly all forms of monosomy are fatal for a child, whereas trisomy can sometimes allow survival but may lead to conditions such as Down syndrome, affecting 1 in 700 births. PGT-A can also identify other chromosomal conditions like Patau syndrome (trisomy 13), Turner syndrome, Klinefelter syndrome, Edward’s syndrome (trisomy 18), among others.

We recommend PGT-A for individuals:

With a history of a previous aneuploidy pregnancy or birth.
Diagnosed with unexplained infertility.
Who have experienced previous failed implantation.
Women over the age of 35.
Facing recurrent miscarriage.

PGT-M

PGT for Monogenic Disease

PGT-M is a screening method designed to identify disorders resulting from a single gene (monogenic disease). In certain cases, one or both parents may carry genes that could be inherited by their child, or there may be a family history of such monogenic diseases, increasing the risk of the child being born with the same condition.

PGT-M can detect various single gene disorders, including but not limited to cystic fibrosis, Fragile X syndrome, sickle cell disease, muscular dystrophy, Huntington’s disease, as well as mutations in BRCA1 & 2 associated with cancer, among others.

We recommend considering PGT-M for parents already diagnosed with or suspected of carrying the conditions. Alternatively, in situations where both partners, including intended parents and donors, share the same recessive gene, PGT-M may be a consideration. However, we strongly advocate for undergoing carrier screening and genetic counselling before making any decisions in such cases.

PGT-SR

PGT for Structural Chromosomal Rearrangement

While other tests focus on assessing the number of chromosomes, PGT-SR examines embryos for abnormal arrangements of chromosomes. This includes instances where segments of chromosomes break off and reattach, either inversely or to a different chromosome section. These rearrangements may or may not have a direct impact on an individual’s health, but they heighten the risk of an embryo having an incorrect amount of chromosome material. This often leads to outcomes like stillbirth, miscarriage, or the birth of a child with significant health issues.

PGT-SR specifically targets Robertsonian translocation, reciprocal and nonreciprocal translocations, and chromosome inversion. We may recommend PGT-SR for individuals experiencing recurrent miscarriage.

Benefits

Preimplantation Genetic Testing

Preimplantation genetic testing offers parents using IVF embryos a means to reduce the likelihood of implantation and pregnancy failures, as well as the chance of having a child with a birth defect. PGT can also help couples avoid the need for repetitive infertility treatments.

For instance, if a couple possesses multiple embryos, and none are genetically normal, they might undergo multiple unsuccessful attempts at embryo implantation. PGT can significantly mitigate the emotional distress and cost associated with such repeated attempts.

Knowing the genetic viability of multiple embryos enables a couple to confidently store embryos for future pregnancies. Another advantage of PGT is family balancing. In cases where a couple already has two male children and desires a girl for their next child, PGT can determine the gender of the embryo by examining the sex chromosome. PFC advises patients to consider PGT for family balancing only if they would be dissatisfied with whatever gender nature might naturally provide for their child.

Procedure

PGT Risks and Considerations

There are certain risks associated with PGT. Perfect Fertility Center exclusively provides PGT for frozen embryos, and the process of freezing and thawing can potentially cause damage to the embryo. Additionally, the biopsy itself poses a small risk of harm to the embryo.

Another risk involves the possibility of false positives or false negatives during testing. This could lead to the implantation of an embryo believed to be genetically healthy that may not be, or conversely, the decision not to implant a healthy embryo that falsely tested negative for genetic health.

FAQ

Have Any Questions?

Here are common questions patients ask about Preimplantation Genetic Testing (PGT) along with detailed answers:

Does PGT harm the embryos in any way?

PGT is generally safe for embryos. The biopsy involves removing a few cells, which usually does not affect the embryo's development. However, like all medical procedures, it carries a small risk of damage.

How reliable are the results from PGT?

PGT is highly accurate, with an accuracy rate of over 95% for detecting chromosomal abnormalities and genetic disorders. However, no test is perfect, and there is a small chance of false results.

Does PGT ensure that my baby will be healthy?

While PGT significantly reduces the risk of genetic disorders and chromosomal abnormalities, it cannot guarantee a healthy baby. It does not test for all possible genetic conditions or environmental factors affecting pregnancy.

Do I need to do anything special to prepare for PGT?

There is no special preparation for PGT itself, but thorough genetic counseling is recommended. Understanding your family history and undergoing genetic carrier screening can also be helpful.

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