Expanded Carrier Screening Before IVF: Why Both Partners Matter

Expanded Carrier Screening Before IVF: Why Testing Both Partners Before You Conceive Matters

Before starting IVF, many couples are offered expanded carrier screening—a genetic test that examines hundreds of inherited conditions in both partners. For couples with no known family history of genetic disease, it can seem unnecessary. In reality, it plays an important role in identifying risks that would otherwise remain hidden.

The test does not look for diseases affecting your own health. Instead, it determines whether you are a carrier of a recessive genetic condition. A healthy person can carry a faulty copy of a gene without experiencing any symptoms because the second, healthy copy continues to function normally.

The same applies to your partner. A child is only at risk if both parents carry a mutation in the same gene. Most carrier couples have no family history and discover their risk only after the birth of an affected child.

Expanded carrier screening identifies this possibility before pregnancy, allowing couples to make informed reproductive decisions. It is recommended for couples planning IVF, those using donor eggs or donor sperm, and especially couples who are related by blood, where the likelihood of sharing the same genetic mutations is significantly higher.

Why Healthy People Can Carry Genetic Diseases Without Knowing

Most serious inherited genetic disorders follow an autosomal recessive inheritance pattern.

This means a child must inherit two faulty copies of the same gene—one from each parent—for the condition to develop.

If you carry only one faulty copy, you remain completely healthy because your normal copy of the gene compensates for it. You may never know you are a carrier.

In fact, almost everyone carries at least one recessive genetic mutation. When healthy individuals undergo expanded carrier screening across hundreds of genes, approximately half are found to be carriers of at least one inherited condition.

A normal family history does not eliminate this possibility. Recessive conditions often remain hidden for generations until two carriers happen to have children together.

What Does Expanded Carrier Screening Test?

Traditional carrier screening focused mainly on diseases associated with specific ethnic groups.

• Tay-Sachs disease in individuals of Ashkenazi Jewish ancestry.
• Cystic fibrosis in people of Northern European descent.
• Thalassaemia in Mediterranean, Middle Eastern, and South Asian populations.
• Sickle cell disease among individuals of African ancestry.

However, modern populations are increasingly diverse, and many people are unaware of their complete ancestry.

Expanded carrier screening removes the need to select tests based on ethnicity. Using a single blood or saliva sample, hundreds of recessive genes are analysed simultaneously, regardless of ethnic background.

This provides a far more comprehensive assessment of inherited genetic risks before pregnancy.

The Numbers That Surprise Most Couples

One of the most surprising findings from expanded carrier screening is how common carrier status actually is.

Around half of all healthy individuals tested on large screening panels carry at least one recessive genetic mutation.

On its own, this is not a cause for concern. The risk only becomes significant when both partners carry mutations in the same gene.

Depending on the population studied and the screening panel used, approximately 1–5% of couples are identified as "at-risk couples," with some studies reporting a rate of approximately one in twenty-two couples.

When both partners carry the same recessive condition, every pregnancy carries:

• A 25% chance of having an affected child.
• A 50% chance of having a healthy carrier child.
• A 25% chance of having a child who inherits neither faulty gene.

These probabilities remain the same for every pregnancy.

Why Expanded Carrier Screening Matters Even More in Certain Populations

Carrier screening is particularly important for couples who are biologically related, such as first cousins.

Related individuals share a larger proportion of their genetic material, making them more likely to carry the same recessive mutations.

As a result, consanguineous couples have a significantly higher likelihood of being identified as at-risk couples.

Inherited conditions commonly seen in many Middle Eastern, South Asian, and Mediterranean populations—including thalassaemia and sickle cell disease—are exactly the types of disorders expanded carrier screening is designed to detect.

For related couples planning IVF, expanded carrier screening provides valuable information before embryos are created.

What Happens If Both Partners Are Carriers?

Being identified as an at-risk couple does not mean you cannot have healthy biological children. Instead, it provides the opportunity to make informed decisions before pregnancy begins.

For couples undergoing IVF, one of the most effective options is Preimplantation Genetic Testing for Monogenic Disorders (PGT-M).

Once the specific genetic condition has been identified, embryos created through IVF with ICSI can be tested before transfer.

Only embryos that are unaffected by the inherited condition are selected for transfer into the uterus.

Other reproductive options may include:

• Using donor sperm or donor eggs.
• Prenatal genetic testing during pregnancy.
• Alternative family-building options based on individual circumstances.

Identifying carrier status before conception provides couples with the greatest number of reproductive choices.

How Is Carrier Screening Different from PGT-A?

Expanded carrier screening and PGT-A are often confused, but they answer two completely different questions.

• Expanded Carrier Screening: Tests the DNA of both parents to determine whether they carry inherited recessive genetic conditions.
• PGT-A (Preimplantation Genetic Testing for Aneuploidy): Tests embryos for chromosome abnormalities such as Down syndrome before embryo transfer.

Carrier screening identifies inherited single-gene disorders that parents may pass to their children, while PGT-A evaluates whether an embryo has the correct number of chromosomes.

A normal PGT-A result does not rule out inherited conditions such as cystic fibrosis or thalassaemia, making carrier screening an important complementary test.

What Does a Negative Result Mean?

A negative expanded carrier screening result significantly reduces the likelihood of carrying many inherited genetic conditions, but it does not eliminate all genetic risk.

No screening panel can test every gene or identify every possible mutation. Some rare genetic changes may not be detected, and certain conditions result from new (de novo) mutations that occur spontaneously during embryo development.

For these reasons, expanded carrier screening should be viewed as a highly reassuring test rather than an absolute guarantee.

It substantially reduces the risk of many serious inherited conditions while acknowledging that no genetic test can eliminate every possibility.

Conclusion

Expanded carrier screening is one of the most valuable genetic tests available before IVF or pregnancy planning. By identifying hidden carrier status before embryos are created, couples gain the opportunity to make informed decisions and reduce the risk of passing serious inherited conditions to their children.

Whether you are beginning IVF, using donor eggs or sperm, or are part of a consanguineous relationship, testing both partners before conception provides valuable information that can shape your treatment plan and future family.

Book a consultation with MMC IVF today to learn whether expanded carrier screening is recommended for your fertility journey and discuss the options available based on your results.