What is genetic carrier screening and should I consider it before pregnancy?

If you’re thinking about starting a family, you may have questions about whether your future children could inherit certain genetic conditions. Genetic carrier screening is a test that can help you understand this risk before pregnancy begins.

What does it mean to be a carrier?

You are a carrier if you have one altered copy of a gene that, when two copies are present, causes a genetic condition. Most carriers are completely healthy - they have no symptoms of the condition themselves. This is because many genetic conditions follow what’s called “recessive inheritance”: you need two altered copies of the gene (one from each parent) to develop the condition.

If both you and your partner are carriers of the same recessive condition, there is a risk that your child could inherit both altered copies and develop that condition. Carrier screening identifies whether you carry these gene changes before you conceive, so you can make informed decisions about your family planning.

What conditions does carrier screening cover?

Carrier screening can test for hundreds of inherited conditions. The most commonly screened conditions vary by ancestry and population, but typically include:

• Cystic fibrosis - affects the lungs and digestive system
• Sickle cell disease - affects red blood cells and oxygen transport
• Thalassaemia - affects haemoglobin production; carriers are usually clinically silent
• Spinal muscular atrophy - affects nerve cells and muscle movement
• Fragile X syndrome - causes intellectual disability
• Tay-Sachs disease - affects the nervous system

Modern carrier screening panels can assess hundreds or even thousands of genes covering a broad range of inherited recessive conditions, including metabolic disorders and other rare diseases. The number of conditions tested depends on which panel you choose.

Who should consider carrier screening?

Information about carrier screening should be provided to every pregnant woman, and ideally it should be performed before pregnancy. This allows couples to learn about their reproductive risk and consider the most complete range of options.

Carrier screening is particularly relevant if:

• You have a family history of an inherited condition
• You and your partner share ancestry from the same ethnic or geographic group, which can increase the chance of carrying the same gene changes
• You want to understand your reproductive risks before conceiving
• You are already pregnant and want information about potential risks to your baby

You may decline any or all screening - it is your choice whether to have the test.

How does carrier screening work?

Carrier screening is usually done with a blood sample, though some tests use a cheek swab (buccal sample) instead. The sample is sent to a laboratory where your DNA is analysed to look for known gene changes associated with inherited conditions.

If you are found to be a carrier for a specific condition, your reproductive partner should be offered testing to understand whether they carry a change in the same gene. If both partners are found to be carriers of the same condition, genetic counselling should be offered to discuss the risk to future children and the options available.

What happens if both partners are carriers?

If both you and your partner are carriers of the same recessive condition, each pregnancy has:

• A 25% chance that the baby will inherit both altered copies and have the condition
• A 50% chance that the baby will be a carrier like you, with no symptoms
• A 25% chance that the baby will not be a carrier and will not have the condition

Knowing this information before pregnancy allows you to consider your options, which may include:

• Proceeding with natural conception and having prenatal diagnosis during pregnancy to find out whether the baby is affected
• IVF with preimplantation genetic testing to select embryos that are not affected
• Using donor eggs or sperm to avoid passing on both copies
• Adoption or deciding not to have children

A genetic counsellor can help you understand these options in the context of your specific situation and values.

When is the best time to have carrier screening?

Carrier screening and counselling ideally should be performed before pregnancy. This gives you the most time to consider your results and make informed decisions about your reproductive options.

However, carrier screening can also be done during pregnancy. If you are already pregnant and concerned about inherited conditions, speak to your midwife or GP about testing options. Some screening tests can be combined with prenatal screening for chromosomal conditions.

What are the limitations of carrier screening?

Carrier screening is very accurate for the conditions it tests, but it has some limitations:

• It cannot test for every possible genetic condition - only those included in the panel
• A negative result does not guarantee a healthy baby - it only means you are not a carrier for the conditions tested
• Some gene changes are easier to detect than others - the test may not identify all possible variants
• It does not detect chromosomal conditions like Down’s syndrome, which are screened for separately during pregnancy

The results should always be discussed with a healthcare professional or genetic counsellor who can explain what they mean for you.

What you can do at Jeen

Jeen offers comprehensive carrier screening options to help you understand your reproductive risks before pregnancy:

Carrier Screening analyses 1,008 genes for inherited recessive disease and is designed for couples planning a pregnancy. The test includes 30-minute genetic counselling to discuss your results and options. An at-home buccal swab is included, or you can opt for a blood draw at one of our collection points (+£40). Results are available within 17-21 working days of sample receipt, interpreted using NHS Genomic Medicine Service-aligned variant interpretation standards.

For a more extensive analysis, CGT - Igenomix Carrier Genetic Test uses whole-exome sequencing to assess 1,993 genes (male) or 2,057 genes (female), covering more than 2,200 inherited recessive conditions. This test includes 30-minute pre-test genetic counselling and provides results in 25 working days. Blood collection is not included in the price: you can arrange your own blood draw at no cost, or use one of our 200+ collection points (+£40) or a home-nurse visit (+£65).

Both tests include genetic counselling to help you understand your results and what they mean for your family planning. If you are already pregnant, Unity Complete Screen offers a combined approach: an 8-condition fetal screen from 9 weeks of pregnancy, plus a 4-condition carrier panel, with a free midwife consultation before you take the test. Results are available in 17-21 working days.