In vitro fertilization (IVF) has helped many couples overcome infertility, and now genetic screening can further improve its outcomes. Incorporating genetic testing for IVF embryos has emerged as an invaluable tool to ensure the healthiest embryos are selected for transfer. This practice, often referred to as IVF embryo screening, involves checking embryos for specific genetic or chromosomal issues before pregnancy. By performing this early embryo health check, doctors aim to transfer only embryos with the best chance of developing into a healthy baby. In this article, we’ll explain what preimplantation genetic testing is, how it works, its benefits and limitations, and who might consider it on their fertility journey.
Understanding Genetic Testing in IVF
During an IVF cycle, preimplantation genetic testing (PGT) allows doctors to analyze embryos for potential genetic problems before implantation. This is a form of embryo genetic testing performed in the lab before an embryo is transferred to the uterus. Many people still refer to it colloquially as PGD testing IVF, but today, “PGT” is the broader term involving all types of embryo genetic analysis. PGT gives doctors a window into the embryo’s DNA, enabling them to identify any genetic abnormalities in IVF embryos so that affected embryos are not used for transfer. By identifying these issues before pregnancy, doctors can avoid transferring embryos that carry serious problems.
It’s important to note that fertility genetic testing in the context of IVF typically refers to testing the embryos themselves, not just the parents. Prospective parents often undergo their own genetic carrier screening beforehand. PGT serves as a quality-control step in IVF, a high-tech embryo screening procedure that increases the likelihood of a successful pregnancy.
Types of Genetic Testing for IVF Embryos (PGT-A, PGT-M, PGT-SR)
Not all genetic tests of embryos look for the same thing. There are three main categories of PGT for embryos, each targeting a different type of genetic issue:
- Preimplantation Genetic Testing for Aneuploidy: PGT-A is essentially an IVF chromosome testing procedure. It examines the embryo’s chromosomes to see if there are any extra or missing ones. Humans typically have 46 chromosomes (23 pairs) in each cell. Embryos with the wrong number of chromosomes often fail to implant, miscarry early, or result in conditions like Down syndrome. PGT-A, sometimes called chromosomal testing in IVF, checks each embryo’s chromosomal makeup to ensure it is euploid before transfer. This helps doctors avoid transferring embryos with abnormalities such as trisomies or monosomies.
- Preimplantation Genetic Testing for Monogenic Disease: PGT-M is targeted genetic testing for inherited diseases caused by single-gene mutations. It was previously known as PGD when used for specific disorders. If one or both parents carry a particular genetic mutation, PGT-M can be performed as an inherited disease screening on the embryos. The embryos are tested for the presence or absence of that specific mutation, so that only embryos free of the disease-causing gene are selected.
- Preimplantation Genetic Testing for Structural Rearrangements: PGT-SR is used when one of the prospective parents has a chromosomal structural rearrangement, such as a translocation or inversion of genetic material. These structural issues don’t always cause health problems in the parent, but they can lead to embryos with unbalanced chromosomes. PGT-SR analyzes embryos to ensure they have the correct amount of chromosomal material despite the parents’ rearrangement.
All three forms of PGT are performed similarly during the IVF process, and in some cases, multiple types can be done on the same embryo sample.
The Genetic Testing Process During IVF
What does adding genetic testing actually entail during an IVF cycle? The genetic testing process during IVF involves a few extra steps integrated into the standard IVF procedure. In a typical IVF cycle, the basic steps are: ovarian stimulation, egg retrieval, fertilization of eggs with sperm in the lab, and culture of embryos for a few days. When PGT is planned, the process continues as follows:
- Embryo Development to Blastocyst: After fertilization, the embryos are grown in the lab incubator for about 5–7 days until they reach the blastocyst stage. A blastocyst is an embryo with ~100 cells and has two parts, an inner cell mass and an outer layer called the trophectoderm. By day 5 or 6, the embryos are ready for biopsy.
- Embryo Biopsy: A highly trained embryologist performs a biopsy on each suitable blastocyst. This involves removing a very small sample of cells (often 5 to 10 cells) from the trophectoderm layer of the embryo. Importantly, the cells that are destined to become the baby are left untouched. The biopsy procedure is delicate and requires technical expertise and special equipment. The embryo, minus the few cells removed, can still continue developing normally. In fact, an embryo can usually afford to lose a few trophectoderm cells without harm. This biopsy is done under a microscope with a tiny needle or laser to gently detach cells.
- Laboratory Genetic Analysis: The cells taken from each embryo are sent to a specialized genetics lab. In the lab, technicians extract the DNA and run tests to examine either the chromosomes or specific genes, depending on the type of PGT being done. Modern techniques such as next-generation sequencing (NGS) are often used to get a detailed read of the embryo’s genetic makeup.
- Results and Embryo Selection: Once the genetic testing results are available, the fertility doctor reviews them and identifies which embryos are genetically suitable for transfer. Each embryo may be categorized as “normal,” “abnormal,” or sometimes “mosaic”/“inconclusive” (in PGT-A, mosaic means a mix of normal and abnormal cells). Embryos that appear healthy and normal would be considered for transfer, while those with significant issues are typically not used.
Though the procedural steps of PGT are well-established: create embryos, biopsy them, test the samples, then use the results to guide embryo selection.
Benefits of Genetic Testing in IVF
By selecting a chromosomally normal embryo, couples can increase the odds that the embryo will implant successfully and lead to a healthy pregnancy. Embryos with the correct number of chromosomes have a much better chance of resulting in a live birth. Especially for patients of advanced maternal age, PGT-A can be helpful in identifying which embryos are euploid (chromosomally normal), since older women’s eggs often produce a mix of normal and aneuploid embryos. Transferring a screened, normal embryo can save time and heartbreak compared to transferring embryos blindly and experiencing failures.
One of the major advantages of PGT is a lower chance of miscarriage. The most common cause of miscarriage in the first trimester is chromosomal abnormalities in the embryo. By using PGT-A as a sort of chromosomal testing in IVF to avoid transferring aneuploid embryos, the risk of miscarriage is reduced. This doesn’t eliminate miscarriage, but it can greatly improve the odds.
Perhaps the clearest benefit of all is the ability to prevent inherited diseases in your children. If prospective parents know they have a serious genetic condition in their family, PGT-M empowers them to select an embryo that is free of that condition. This is life-changing for families with hereditary illnesses. Instead of facing a 25% or 50% risk of having an affected child, they can reduce that risk to near zero by testing embryos and only implanting those without the disease gene. PGT-M can currently be used to avoid over 1,700 different genetic conditions that might otherwise be passed on. This means thousands of inherited diseases can be screened at the embryo stage. For couples who carry these conditions, this technology offers immense peace of mind and the chance to spare their children from the disease.
Who Should Consider Genetic Testing Before IVF?
If either partner has a known genetic disease or is a carrier of one, they should consider PGT-M. For example, if you both carry the gene for an autosomal recessive disease like cystic fibrosis, each child has a 25% chance of having the disease. PGT-M can eliminate that risk by screening embryos. Similarly, if one partner has a dominant disease (like Huntington’s disease) or an X-linked condition, testing can ensure an unaffected embryo is chosen. Genetic testing for inherited diseases is especially valuable if you’ve experienced a previous pregnancy or child affected by a genetic condition.
As a woman’s age increases, the percentage of her eggs (and thus embryos) with chromosomal abnormalities rises dramatically. Women 38+, and especially over 40, often produce many aneuploid embryos, which leads to lower success rates and higher miscarriage rates. PGT-A is commonly recommended for IVF patients of advanced maternal age to help identify any chromosomally normal embryos among those created. If you are 35 or above, and particularly if you are over 40, genetic embryo screening can be a useful tool to screen for chromosomal abnormalities and improve your chance of a successful IVF.
Couples who have suffered two or more miscarriages may consider PGT-A in subsequent IVF attempts. Recurrent miscarriage can sometimes indicate an underlying issue with embryo quality. By transferring only screened normal embryos, the risk of another miscarriage due to a random chromosomal error is reduced. This approach has helped some patients with repeated losses carry a pregnancy to term. Of course, not all miscarriages are genetic, but if you’ve had multiple losses, it’s worth discussing PGT-A with your provider as part of your plan.
If you have done IVF in the past and had multiple failed cycles or embryos that didn’t implant, PGT might be beneficial in your next attempt. Sometimes the issue in prior failures was unseen genetic problems in the embryos. Screening can give insight into whether your embryos were aneuploid, and ensure that this time only an embryo with normal chromosomes is used. Additionally, for those with unexplained infertility, PGT-A can at least ensure embryo aneuploidy isn’t the culprit behind failed implantation. Couples who have gone through numerous unsuccessful fertility treatments often add PGT in hopes of improving their chances. The decision to pursue genetic testing with IVF should be individualized. PGT is being widely used these days to prevent the transfer of abnormal embryos that would likely not lead to a successful pregnancy or that might result in miscarriage or a child with a genetic disorder.
Deciding whether to include genetic testing in your IVF cycle is a significant choice. It’s not one you have to make alone. It’s highly recommended to have a detailed discussion with your fertility specialist, a fertility consultation focused on PGT. Your doctor will review your individual case and help determine if embryo testing is appropriate. A fertility specialist can walk you through the available procedures and advise you based on the latest science and your personal risk factors. They will consider things like your age, diagnosis, number of embryos expected, and any known genetic issues when making a recommendation.
It’s worth mentioning that not all fertility clinics offer PGT, since it requires expertise and technology that some smaller clinics may lack. You may need to be at a fertility treatment center that has the capability to do embryo biopsies and work with genetic labs. For example, at IVF Center Hawaii, the team is experienced in advanced procedures like PGT and can provide this service as part of IVF. Choosing a reputable clinic with PGT experience can ensure you receive proper counseling and technical care throughout the process.
Genetic testing before IVF is a powerful option that has evolved significantly in the past decade. It allows for IVF embryo screening at a molecular level, giving many families hope of increased success and healthy outcomes. If you’re considering IVF, it’s wise to educate yourself on PGT and discuss it with your doctor. For some, it can make all the difference by preventing heartbreak and improving odds; for others, it may be an unnecessary add-on. By understanding what PGT involves, its benefits, and its limitations, you can make an informed choice.
Sources
- Human Fertilisation & Embryology Authority (HFEA) – “Approved PGT-M and PTT conditions.”
- Mayo Clinic – “In vitro fertilization (IVF)” (Overview and Risks section on preimplantation genetic testing)
- IVF Center Hawaii – “Pre-implantation Genetic Testing (PGT) Services” (Fertility Institute of Hawaii)
- Women & Infants Fertility Center – “A Guide to Preimplantation Genetic Testing (PGT).”