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25 January 2021

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Preimplantation genetic testing for genetic conditions

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Everything you need to know about testing for genetic disorders, according to a doctor.

At a glance:

  • Screening tests for genetic disorders are encouraged but voluntary
  • The most common screening tests are done during the first trimester of pregnancy
  • Genetic testing can also assist couples battling unexplained infertility

Having a family is an exciting time, but – as with all the best things in life – there is always an element of risk. Risk of struggling to fall pregnant, risk of losing a pregnancy, and risk of medical complications along the way. These days, we’re fortunate to have access to screening for many disorders. If you’re thinking about starting a family, it’s good to be aware of what tests are available to help assess your chances of having a healthy baby.

Why get tested?

There are lots of inherited disorders (more than 3,000 in fact) that on their own are rare, but collectively affect approximately 1% of births. If you or your partner are a carrier of these genes, it’s possible you (or your family) may have no idea, so it’s worth discussing with your doctor or a genetic counsellor to decide whether testing is right for you.

Risks factors generally stem from your age, lifestyle and medical history. The chance of conceiving a baby with a genetic disorder is higher if:

Often these tests can be done via a simple blood test or ultrasound, and although many doctors encourage women to undertake genetic testing, it remains completely voluntary - with many couples choosing not to go down that route.

 So, what tests are available?

“Probably the most common test during pregnancy is done in the first trimester where many couples are screened for Down syndrome,” explains IVF Australia’s Clinical Director and UNSW Professor Gavin Sacks.

This is usually done in one of two ways:

  • The standard first trimester combined screening test is the combination of results from a blood test taken at around 9-12 weeks and an ultrasound at 11-13 weeks to detect if your baby is at an increased risk of having Down syndrome or what’s called Trisomy 18 – also known as Edwards syndrome. This testing is widely encouraged by hospitals.
  • NIPT (non-invasive prenatal testing) is a newer screening model that provides information about the risk of a baby presenting with genetic conditions by examining the DNA through their mother’s blood. It can be done any time from 9 weeks into a pregnancy and is more accurate than combined first and second-trimester screening. It does, however, cost more - as the test isn’t currently covered by Medicare.  

Not pregnant yet? Dr Sacks explains that screening for Down syndrome and other chromosomal conditions is possible even before a couple conceives if you’re having fertility treatment such as in vitro fertilisation (IVF). “You can test embryos before they’re even implanted using a technique called PGT (pre-implantation genetic testing),” he explains.

This procedure – usually undertaken at a fertility clinic – means specific embryos can be selected for transfer during an IVF cycle, maximising the chance of having a healthy baby.

Screening tests vs diagnostic tests

It’s important to note that although genetic screening tests can provide information on the likelihood of health issues, they don’t offer up a definite diagnosis. This is worth being aware of so you know what to expect when you get your results, as results from a screening test aren’t delivered as a “yes” or a “no”, but rather as “increased risk” or “low risk”.

If a screening test suggests an increased risk for a particular condition, a diagnostic test can offer a little more clarity. Some of these diagnostic tests however are a little more invasive and carry a small risk of complications including miscarriage

It’s worth noting that 1 in 20 women are told there is a complication in her pregnancy, and many will go on to have a normal pregnancy. Diagnostic tests can assess whether you or your baby might need specialist treatment or even surgical correction while the baby is still in the uterus.

Genetic testing and fertility

Many couples struggling to conceive choose to undergo genetic testing to see if there are any underlying issues as to why a pregnancy won’t take.

“Often unexplained infertility happens because the genetic quality of a couple’s embryos is abnormal,” explains Dr Sacks. “Usually these are chromosomal abnormalities.”

This is when procedures like pre-implantation genetic testing (PGT) can be offered, which have helped many couples conceive healthy babies despite more challenging genetic odds.  

If you suspect you may have a genetic or chromosomal abnormality, see your GP or fertility specialist for support. They can organise genetic counselling and help you decide what tests are right for you.

 

Sources

https://www.ivf.com.au/about-fertility/how-to-get-pregnant/preconception-screen

https://www.betterhealth.vic.gov.au/health/healthyliving/pregnancy-prenatal-tests

https://www.thewomens.org.au/health-information/pregnancy-and-birth/now-you-are-pregnant/genetic-testing-in-pregnancy

https://www.healthdirect.gov.au/edwards-syndrome-trisomy-18

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