Healthy couples can still share hidden genetic risks — and not know it until pregnancy. Could your genes affect your future family?
In this webinar, María Puig Peral, Specialist in Molecular Genetics at Nuuma Genetics, explains what genetic carrier screening is, why it matters before trying to conceive or starting IVF, and how it can help couples make more informed fertility decisions.
You’ll learn how carrier screening can uncover inherited risks early, support donor matching, and clarify when further steps such as PGT may be worth considering.
Hosted by: Barbara Scott, Chair of the Association of Reproductive Reflexologists & Founder of Seren Natural Fertility
Genetic carrier screening identifies whether a person carries genetic variants associated with certain hereditary diseases even when they have no symptoms, no personal history of illness, and no known family history.
Many people who carry a disease-causing genetic change have no symptoms at all. They may have no personal history of illness and no known family history either. That is what makes carrier screening relevant in fertility care: it is designed to identify whether someone carries pathogenic variants linked to certain inherited conditions before those variants are unknowingly passed on to a child.
The test focuses on monogenic disease, meaning disorders caused by changes in a single gene. In reproductive medicine, the main concern is usually conditions inherited in an autosomal recessive or X-linked recessive pattern. There are approximately 1,300 monogenic diseases, and approximately 1 to 2 in every 1,000 couples are at risk of having a child affected by an autosomal recessive or X-linked disease. Together, these conditions affect around 2.5 in every 1,000 newborns.
A carrier is not the same as a person with the disease. In recessive conditions, carriers are often healthy because they have one altered copy of a gene and one normal copy. These heterozygous carriers usually do not experience symptoms, but they can still pass the altered gene to their children.
The risk becomes significant when both members of a couple carry a pathogenic variant in the same gene for an autosomal recessive disease. In that situation, each pregnancy has a 25% chance of producing an affected child. That is the central reason carrier screening is done before conception or during fertility treatment: it identifies couples with increased genetic risk before a pregnancy is established.
X-linked inheritance works differently. If a woman carries a pathogenic variant in an X-linked gene, there is a 50% chance she will pass the mutated gene to her daughters, who will be carriers, and a 50% chance she will pass it to her sons, who will be affected by the disease. In practice, that can alter reproductive planning even when only one partner is a carrier.
Carrier screening is most useful as a preconception screening tool. For patients considering IVF, that means it ideally happens before pregnancy and as early as possible in the treatment pathway. It can also be used during reproductive treatment, or later if testing was not done earlier, but earlier testing gives patients more room to make decisions.
Several groups are especially relevant candidates:
The test also has value in donor conception. When donor eggs or sperm are being used, genetic matching can be performed between donor and recipient based on the genetic panel. The goal is to reduce the risk of having a child affected by a disease included in the panel or by variants carried by the recipient.
That matching step matters because risk in reproductive genetics is not based only on one person’s result. It depends on the combination of both genetic profiles. A result that seems low-risk with one partner may need to be reconsidered with a new partner.
A key practical decision is how broad the screening should be. Advances in Next Generation Sequencing now allow hundreds of genes to be analyzed through a single test, making broader screening possible than in the past.
The basic panel includes 15 genes associated with autosomal recessive inheritance in men. In women, that same panel also includes additional genes associated with X-linked disorders. The expanded carrier screening panel includes everything in the basic panel plus additional genes associated with autosomal recessive disorders.
For patients, the difference comes down to breadth and residual risk. A broader panel reduces the risk of having a child affected by a severe genetic disorder more than a narrower one does.
Still, broader does not mean complete. Even the most extensive panel cannot eliminate risk entirely.
Some important conditions require complementary testing rather than standard sequencing alone. Carrier screening may therefore include additional analyses such as multiplex ligation-dependent probe amplification of the HBA gene and SMN1 studies.
For the HBA gene, this testing looks for gains or losses of genetic material and helps determine whether a person is a carrier of alpha thalassemia, a condition characterised by microcytic anaemia or hypochromic anaemia. For SMN1, multiplex techniques are used to detect microdeletions or microduplications, especially in exons 7 and 8, and this supports the diagnosis of patients with suspected spinal muscular atrophy.
In women, the screening also includes analysis of the FMR1 gene and CTG triplet expansion. For patients, the key point is not the laboratory method itself but the reason these add-ons exist: some disease-causing changes are not captured well by a standard sequencing approach alone, so complementary methods are used to improve detection.
Carrier screening is not done for information alone. Its value lies in what happens next.
In a compatibility study, the woman is first offered carrier screening for autosomal recessive disease. If no pathogenic or likely pathogenic variant is found in the genes included in the panel, the couple is considered at low risk of passing on a recessive disorder, and treatment can continue. The risk of having a child affected by monogenic disease is significantly reduced, but not completely eliminated.
If the woman carries a pathogenic or likely pathogenic variant in a gene included in the panel, carrier testing is then recommended for her partner. If she carries a pathogenic or likely pathogenic variant in an X-linked gene, preimplantation genetic testing is recommended.
When both partners share a pathogenic or likely pathogenic variant in the same gene, the couple faces a 25% probability that their children will be affected by the disease. At that point, reproductive options may include:
This is where genetic counselling becomes essential. The test result does not dictate one path. It clarifies the risk so patients can choose among personalised reproductive options with a full understanding of what is at stake.
Carrier screening has a particularly practical role in donor conception. If no variants are shared in the same genes between donor and recipient, the match is considered low genetic risk and gamete donation can proceed. In that situation, the remaining risk is tied to the limitations of the detection techniques rather than a known shared variant.
There is an additional safeguard in oocyte donation. If the donor is a carrier of a pathogenic variant in an X-linked gene, she is considered a high genetic risk donor and should be excluded.
For all its value, carrier screening has limits, and understanding those limits is part of making a good decision. Carrier screening is a screening tool, not a diagnostic test. It does not determine whether a person has a disease, and it cannot guarantee that a future child will be unaffected by every genetic condition.
The biggest concept patients need to understand is residual risk. A low-risk result does not mean zero risk. Risk remains because detection techniques have limitations, some disease-causing variants may not be detectable by the technology or analytical method used, and some variants have not yet been described. In some cases, interpretation also depends on scientific knowledge that continues to evolve.
That is why informed consent and genetic counselling are built into the process. Results need context. A negative result lowers risk. It does not erase it.
One practical advantage of carrier screening is that the individual result does not expire. A person’s genetic profile remains the same over time, so the test itself is considered valid for life.
What can change is the reproductive pairing. If someone has screening with one partner and later has a new partner, the individual result is still valid, but the couple-based risk may need to be reassessed. That is because recessive risk depends on whether both people carry variants in the same gene.
Timing also matters in another way. If embryos have already been created, carrier screening may no longer answer the most immediate question before transfer. In that setting, preimplantation genetic testing of the embryos themselves may be the more relevant next step.
Carrier screening is powerful, but it is not a substitute for a full clinical evaluation. Patients with recurrent pregnancy loss, repeated failed IVF cycles, or a complicated reproductive history may still need a broader review of their medical background. In some cases, an autosomal recessive disorder could be contributing, but the history has to be examined carefully.
Genetic counselling remains central because management depends on the patient’s history and circumstances. The same laboratory result can have different implications depending on family history, treatment stage, donor use, and prior pregnancy outcomes.
For IVF patients, genetic carrier screening is best understood as an early planning tool rather than a final answer. It can guide partner or donor matching and open the door to options such as preimplantation genetic testing, prenatal diagnosis, or egg donation when a shared risk is found. It can significantly reduce the chance of severe inherited disease in offspring, but it cannot completely eliminate that possibility.
Done early and paired with thoughtful genetic counselling, carrier screening gives patients something fertility treatment often depends on: clearer choices before the next step is taken.
Genetic carrier screening is recommended before pregnancy, during the reproductive treatment process, or before the birth of a child if testing has not already been done. Ideally, it is considered as early as possible, before birth and early in the treatment pathway.
It should be presented at the first visit. That first consultation is the starting point because the test is important for assessing disorders and screening.
The full medical history and background must be reviewed first. In cases such as four confirmed chromosomal losses, including trisomy 16 and 3, a chromosome 8 deletion, a recent euploid embryo loss at 7 weeks, and normal karyotyping twice, it is possible that an autosomal recessive disorder is contributing, but more history is needed. The same applies when there are recurrent miscarriages or repeated failed IVF cycles even if all other tests are normal: the medical history needs to be reviewed in detail.
This depends on the clinic and the patient’s personal history. Management is individualized for each patient.
Yes. In Spain, the fertility society recommends carrier screening on donors because of the prevalence, penetrance, or severity of certain disorders. Examples include cystic fibrosis, spinal muscular atrophy, and alpha thalassemia. This screening is recommended and mandatory for gamete donors.
The genetic screening is performed with blood and does not consider sperm.
The basic panel includes genes for higher-prevalence disorders related to autosomal recessive disease. The expanded panel includes the genes covered by the basic panel plus additional genes.
Patients may choose the expanded panel when they have a family history or when they want to reduce residual risk through a broader panel.
