PGD (Preimplantation Genetic Diagnosis): Preventing Inherited Genetic Conditions

Understanding PGD (PGT-M) and Why It Matters

Preimplantation Genetic Diagnosis, now more precisely called PGT-M (Preimplantation Genetic Testing for Monogenic disorders), is a laboratory technique used alongside IVF to examine embryos for a specific, known inherited genetic condition before a pregnancy begins. It was developed for couples who already know that a serious single-gene disease runs in their family and who want the option to reduce the chance of passing that disease on to a child.

PGT-M does not create or alter genes. It identifies, among the embryos created during an IVF cycle, which ones carry the specific disease-causing gene change that has already been identified in the family, and which ones do not. This information allows a physician and the intended parents to choose to transfer embryos that are not affected by the condition being tested for.

This form of testing exists strictly as a medical tool for disease prevention. It is offered only when there is a documented, known genetic risk in the family, confirmed through prior genetic testing or counseling, not as a general screening option for every IVF patient.

PGT-M Compared With PGT-A

PGT-M is often confused with PGT-A (Preimplantation Genetic Testing for Aneuploidy), but the two tests answer different questions. PGT-A looks at the overall number of chromosomes in an embryo to check whether any are missing or duplicated, a common cause of implantation failure and miscarriage that becomes more frequent with maternal age.

PGT-M, by contrast, looks for one specific gene mutation that has already been identified in a parent or in a close family member through medical genetic testing. It requires laboratory preparation in advance, using DNA samples from the affected family members, so that the exact mutation can be tracked accurately in each embryo. PGT-M and PGT-A can sometimes be performed together on the same embryo biopsy when both chromosome health and a known inherited condition need to be assessed.

Inherited Conditions PGT-M May Help Prevent

Single-Gene Disorders

PGT-M is most commonly used for serious conditions caused by a change in a single gene, including thalassemia, cystic fibrosis, sickle cell anemia, Huntington’s disease, spinal muscular atrophy, and Fragile X syndrome. These conditions can significantly affect a child’s health and, in many cases, are life-limiting or require lifelong medical care.

Structural Chromosomal Rearrangements

Some individuals carry a balanced chromosomal rearrangement, such as a translocation, which does not usually affect their own health but can lead to embryos with unbalanced chromosome material. This is a recognized cause of recurrent pregnancy loss and can also be assessed through a related preimplantation genetic testing method.

Sex-Linked Inherited Diseases

Certain serious inherited diseases, such as hemophilia and Duchenne muscular dystrophy, are caused by a specific gene change on a chromosome that follows a distinct inheritance pattern within families. When the exact disease-causing mutation is known, PGT-M can test embryos directly for that mutation, allowing families with a documented history of the disease to reduce the risk of a child being born with the condition. This use of testing is strictly about identifying and avoiding a specific, serious illness.

HLA Matching for a Sibling Who Is Ill

In rare and carefully evaluated circumstances, PGT-M can be combined with HLA typing to identify an embryo that is both free of a known familial disease and a tissue match for an existing child who requires a stem cell transplant, such as for certain blood disorders. This application is offered only within strict ethical and medical guidelines.

Who Should Consider PGT-M

PGT-M is intended for a specific group of patients rather than the general IVF population. It is generally considered by:

• Couples where one or both partners are confirmed carriers of a known single-gene disorder
• Families with a documented history of a serious inherited genetic disease
• Parents who have already had a child affected by a diagnosed genetic condition
• Couples experiencing recurrent pregnancy loss linked to a confirmed structural chromosomal rearrangement
• Families seeking a tissue-matched sibling for a child with a serious illness treatable by stem cell transplantation

A referral to a clinical geneticist or genetic counselor, along with confirmed carrier testing, is typically required before PGT-M can be planned, since the laboratory must know the exact mutation to search for in each embryo.

How the PGT-M Process Works

PGT-M is carried out as part of a standard IVF cycle using intracytoplasmic sperm injection, or ICSI, which helps reduce the risk of extra genetic material from surrounding sperm interfering with the test results.

• Ovarian stimulation and egg retrieval proceed as in a standard IVF cycle
• Eggs are fertilized using ICSI to support accurate genetic analysis later
• Embryos are cultured in the laboratory until they reach the blastocyst stage, usually around day five or six
• A small number of cells are carefully removed from the outer layer of the blastocyst, known as the trophectoderm, in a process called biopsy
• The biopsied embryos are frozen while the biopsy sample is sent for molecular genetic analysis using techniques such as PCR or next-generation sequencing
• Results identify which embryos are unaffected by the specific condition being tested for
• An unaffected embryo is selected for transfer in a subsequent frozen embryo transfer cycle, with any remaining unaffected embryos stored for future use

Accuracy, Safety, and Honest Limitations

Trophectoderm biopsy is a well-established technique that is considered safe when performed by an experienced embryology team, and current evidence does not show that it harms embryo development when done correctly. As with any medical procedure, no method is entirely without risk, and outcomes depend on individual circumstances.

PGT-M is highly accurate for detecting the specific mutation it is designed to test for, but no genetic test is completely error-free. Laboratory results can occasionally be inconclusive, and a small chance of misdiagnosis exists with any preimplantation genetic technology. PGT-M also does not screen for every possible genetic or medical condition, only the specific disease it has been set up to detect in that family.

Choosing an embryo unaffected by the tested condition does not guarantee a healthy pregnancy or a healthy child, since other unrelated medical or developmental factors can still occur. For this reason, confirmatory testing during pregnancy, such as amniocentesis or chorionic villus sampling, is often recommended even after a favorable PGT-M result.

Frequently Asked Questions

Does PGT-M test for every genetic disease?

No. PGT-M is designed to detect one specific, previously identified mutation in a family. It does not provide a general health guarantee and does not screen for unrelated conditions unless additional testing is specifically arranged.

Is the embryo biopsy harmful to the embryo?

Current evidence suggests that trophectoderm biopsy, when performed by trained embryologists, does not reduce the embryo’s ability to implant or develop when the procedure is carried out correctly.

How long does it take to set up PGT-M testing?

Because the laboratory must first develop a test specific to the family’s known mutation, preparation can take several weeks before an IVF cycle begins. Early consultation with a genetic counselor is recommended.

Will PGT-M guarantee a healthy baby?

No test can guarantee a healthy baby. PGT-M reduces the risk of a child inheriting the specific condition that has been tested for, but it cannot rule out all other genetic, developmental, or health factors.

Discuss Your Family History With Our Team

If a serious inherited genetic condition runs in your family, or you have concerns after a previous pregnancy or diagnosis, a conversation with a fertility and genetics team can help clarify whether PGT-M may be appropriate for your situation. GynoLife IVF Center, based in Cyprus, works with patients to review family and genetic history, coordinate carrier testing, and explain each stage of the IVF and preimplantation testing process in clear, honest terms. Reaching out for a consultation is a good first step toward understanding your options.