Genetic testing and screening

Genetic testing and screening can help you find out of your baby could develop certain genetic conditions (passed on through your genes). This is usually done when there is a family history of a major health problem that is likely to be passed on to the baby.

What is genetic testing?

Genetic testing helps to find out if a person’s genes or chromosomes may be linked to a health condition; it can also identify changes in a person’s genes. The procedure can be done before a pregnancy, during a pregnancy, or later in life. 

Genetic testing is not available for every condition. It is also not usually possible unless the gene change is already known in the family. Lastly, results of the testing are not always clear. Because of these and other limitations with genetic testing, and because not all health conditions are genetic, a “normal” result does not guarantee that a child will be healthy.

Who should consider genetic testing?

You may want to consider genetic testing if:

• you or your partner is at risk of passing on a genetic condition (like cystic fibrosis)
• you or your partner has a chromosome condition, or has a child with a chromosome condition (like Down syndrome)
• you are a woman over 35, and therefore more at risk of having a child with a chromosome condition because of your age

Genetic testing before pregnancy

Embryos created using in vitro fertilization (IVF) can be tested for a specific genetic condition before they are transferred to your womb (uterus). This test is called Preimplantation genetic diagnosis (PGD). If testing shows embryos carry a genetic condition, those embryos are not usually transferred.

Advantages of PGD

• PGD is very accurate and is the earliest way to detect a genetic or chromosomal condition before birth.
• Finding a genetic condition through PGD may help in decision making.
• PGD may also increase the possibility of a pregnancy and live birth, because genetic and chromosomal conditions often result in natural miscarriages.

Disadvantages of PGD

• PGD is usually carried out only if the genetic change for the specific condition has already been found in one or both partners through earlier genetic testing.
• PGD is intended to detect specific genetic conditions. But testing may reveal an unexpected chromosome problem in the embryo, unrelated to family history.
• The costs of PGD are usually added to the costs for fertility treatments, and will depend on the specific test.
• PGD does not guarantee that an embryo will implant or that a full term pregnancy will result. Miscarriage can still happen.

Genetic screening and testing during pregnancy

Prenatal screening

Prenatal screening is done before a baby is born. It detects pregnancies with a higher chance of being affected with a chromosome condition (like Down syndrome) or birth defects (like Spina bifida). A screening test can only estimate risk and cannot confirm if the developing foetus has one of these conditions.

Some screening options include: integrated prenatal screening (IPS), first trimester screening (FTS), maternal serum screening (MSS-quad), and obstetrical ultrasound.

Questions to consider before prenatal screening:

• How do I feel about having a child with one of the screened conditions?
• Do I want to know if my pregnancy may be affected with one of these conditions?
• If my screening result is positive (meaning my baby is at higher risk), would I consider prenatal genetic testing to find out if my child will be affected?

Prenatal genetic testing

Prenatal genetic testing means testing a foetus (baby before it is born) for genetic changes. Options include amniocentesis and chorionic villus sampling (CVS).

• Amniocentesis: Usually carried out between 15–18 weeks of pregnancy. It has a 0.5-1% risk for complications, including miscarriage.
• CVS: Usually carried out between 10–12 weeks of pregnancy. It has a 1-2% risk for complications, including miscarriage.

Common feelings about testing

Not everyone who has genetic testing or screening will have the same reaction. People within a family may have very different feelings.

• Some people may worry about what the test result may show, or how they will react to the test result.
• Others may feel relief that they were able to inform themselves. The results of genetic testing may help these people decide what to do next.
• People who are at risk of having a child with a genetic condition may feel anxious or overwhelmed at the thought of passing it onto the next generation.
• Others may be comfortable with the risks but want to learn about their options.
• People undergoing fertility treatments or prenatal testing may feel stress because of the risk of the procedures, the decisions that they may face, the future health of their baby, financial strain, and relationship pressures.

Getting support and advice

Planning a pregnancy can cause a lot of worry if you are concerned about a genetic condition that can be passed on to your children. The results of a genetic test can have a major impact on your life and the lives of your family members. You should consider talking to your doctor or getting genetic counselling before going ahead with testing.