When should couples consider carrier screening before trying for a baby?

Carrier screening is a type of genetic test that can tell you whether you carry a gene change that could be passed on to your children. Most carriers are healthy and have no symptoms, but if both partners carry a change in the same gene, there is a risk their child could inherit a genetic condition.

Understanding your carrier status before trying for a baby gives you time to consider all your options and make informed decisions about your pregnancy. This article explains when carrier screening makes sense and what it involves.

What does being a carrier mean?

Many genetic conditions follow what is called an autosomal recessive inheritance pattern. This means a child needs to inherit two copies of a gene change - one from each parent - to develop the condition.

If you carry one copy of a gene change, you are called a carrier. Carriers usually do not have the condition themselves because they have one working copy of the gene. However, if both partners are carriers for the same condition, there is a one-in-four (25%) chance with each pregnancy that their child will inherit both gene changes and develop the condition.

Common recessive conditions include:

• Cystic fibrosis - affects the lungs and digestive system
• Sickle cell disease - affects red blood cells and oxygen transport
• Thalassaemia - affects how the body makes haemoglobin
• Spinal muscular atrophy - affects the nerves controlling muscle movement

Carrier rates vary by condition and ethnicity, but many people carry at least one gene change without knowing it. For spinal muscular atrophy, the carrier frequency is approximately one in 40 to one in 60 people.

Who should consider carrier screening before pregnancy?

The American College of Obstetricians and Gynecologists recommends that information about carrier screening should be provided to every pregnant woman, and ideally before pregnancy. Carrier screening and counselling performed before pregnancy enables couples to learn about their reproductive risk and consider the most complete range of options.

You may particularly want to consider carrier screening if:

• You have a family history of a genetic condition, even if you do not have symptoms yourself
• Your partner has a family history or is known to be a carrier for a genetic condition
• You belong to an ethnic group with a higher carrier rate for certain conditions - for example, Ashkenazi Jewish ancestry (Tay-Sachs disease, Gaucher disease), Mediterranean or Asian ancestry (thalassaemia), or African or Caribbean ancestry (sickle cell disease)
• You are related to your partner - cousins or other blood relatives have a higher chance of carrying the same gene changes
• You want to understand your genetic risks as part of planning a family

You do not need a family history to be a carrier. Many carriers are the first person in their family to be identified, and screening can be valuable even without known risk factors.

What happens during carrier screening?

Carrier screening usually involves a blood sample or a cheek swab. The sample is sent to a laboratory, where it is tested for gene changes associated with inherited conditions.

Screening panels vary in size. Some test for a small number of common conditions, while expanded panels can screen for hundreds or even thousands of genes. The results typically take several weeks.

If you are found to be a carrier for a specific condition, your reproductive partner should be offered testing. If both partners are found to be carriers of the same genetic condition, genetic counselling should be offered to discuss potential outcomes and options.

When is the best time to have carrier screening?

The ideal time for carrier screening is before you start trying for a baby. Testing before pregnancy gives you and your partner time to:

• Understand your results without the pressure of an ongoing pregnancy
• Discuss what the findings mean for your family planning
• Consider all available reproductive options, including IVF with genetic testing of embryos (pre-implantation genetic diagnosis), using donor eggs or sperm, or adoption
• Arrange follow-up testing or specialist appointments if needed

If you are already pregnant, carrier screening is still possible and can provide important information. However, the time available to consider options is shorter, and some choices (such as pre-implantation genetic diagnosis) are no longer available for that pregnancy.

What conditions are screened?

Carrier screening panels can test for a wide range of conditions, from common disorders to rare diseases. The number of conditions included varies between different tests.

Standard panels often include:

• Cystic fibrosis
• Spinal muscular atrophy
• Sickle cell disease and thalassaemia
• Fragile X syndrome (a common cause of inherited learning disability)

Expanded panels may screen for hundreds of additional conditions, including:

• Metabolic disorders such as phenylketonuria or maple syrup urine disease
• Neuromuscular conditions
• Blood and immune system disorders
• Conditions affecting growth and development

Your healthcare provider or genetic counsellor can help you understand which panel is most appropriate for your circumstances.

What do the results mean?

Carrier screening results typically fall into one of three categories:

Negative (not a carrier) - You do not carry a detectable gene change for the conditions tested. This reduces (but does not eliminate) the risk that your child will have one of those conditions.

Positive (carrier identified) - You carry one copy of a gene change associated with a genetic condition. If you are a carrier, your partner should be tested. If your partner is not a carrier for the same condition, your child will not be affected by that specific disorder, although they may also be a carrier.

Both partners are carriers - If both you and your partner carry changes in the same gene, there is a one-in-four (25%) chance with each pregnancy that your child will inherit both changes and have the condition. Genetic counselling can help you understand the specific condition, its severity, available treatments, and your reproductive options.

No test can screen for every possible genetic condition. A negative result is reassuring but does not guarantee that your child will not have a genetic disorder.

What you can do at Jeen

Jeen offers comprehensive carrier screening options for couples planning a pregnancy.

Our Carrier Screening panel tests 1,008 genes for inherited recessive diseases, with results typically available within 17-21 working days of the laboratory receiving your sample. The test includes an at-home buccal swab, so you can collect your sample conveniently at home (an in-clinic blood draw is available for an additional £40). Thirty-minute genetic counselling is included with every test, giving you time to discuss your results and what they mean for your family planning. Variant interpretation follows NHS Genomic Medicine Service standards.

For more extensive screening, the CGT - Igenomix Carrier Genetic Test uses whole-exome sequencing to analyse 1,993 genes (male) or 2,057 genes (female), covering more than 2,200 inherited recessive conditions. This test also includes 30-minute pre-test genetic counselling, with results reviewed by your genetic counsellor within 25 working days of the laboratory receiving your sample. The NHS newborn blood-spot screening programme tests for a small, fixed set of conditions; these expanded panels cover many more, helping you understand a broader range of genetic risks. Blood collection is not included in the price - you can arrange a blood draw at one of our 200-plus partner collection points (£40) or book a home-nurse visit (£65).

Both tests give you detailed information about your carrier status before you conceive, so you can make informed choices about your pregnancy with professional genetic counselling support.