Pre Pregnancy / Early Pregnancy Genetic Carrier Screening

Written by

Rob Buist

Published on


I recommend that you consider genetic carrier testing before you fall pregnant for the first time or, failing that, in early pregnancy. There are a small number of rare or very rare conditions that can be harmful to your baby but are not part of the usual pregnancy genetic testing. The main focus of our routine testing during pregnancy is Down syndrome and a number of other genetic and structural problems (e.g. cleft lip or spina bifida).

Conditions like Cystic Fibrosis (a severe disorder that mainly affects the lungs), Fragile X Syndrome (a cause of intellectual disability) and Spinal Muscular Atrophy – SMA – (a cause of muscle weakness) have not been routinely tested for during your pregnancy until recently.

The thing about these conditions is that you or your partner could be carriers for these conditions without being affected yourselves or even having a family history of them. However if you are both carriers (e.g. Cystic fibrosis) or the mother is a carrier (Fragile X) it is possible for the baby to be affected. If one or other of you is a carrier we can then offer you appropriate testing of your baby relatively early on in your pregnancy (or even before the pregnancy if you are going through IVF). Before you fall pregnant is by far the best time to do this testing.

As these tests are of your own genetic makeup, you only need to do them once in your life.

We can now offer such testing because it is available although Medicare does not help out with the cost.

Please also remember there is also a number of what we call autosomal recessive conditions (e.g. Tay Sachs Disease) that affect members of the Ashkenazi Jewish community so it is very important that if you and your partner are Jewish at least one of you has undergone testing for these conditions prior to pregnancy or, if needs be, early in pregnancy.

Could I be a carrier?


No. of people who are carriers

No. of people affected by the condition

Cystic Fibrosis

1 in 25 1 in 2,500
Fragile X 1 in 150 1 in 4,000
SMA 1 in 40 1 in 6,000 to 1 in 10,000


What is Cystic Fibrosis (CF)?

CF is an inherited condition affecting breathing and digestion. CF causes abnormally thick mucus resulting in recurrent infections that damage the lungs. People with CF require daily physiotherapy to clear mucus from their lungs, frequent courses of antibiotics and need to take medicine to aid digestion. There is no cure for CF. Before current treatment (including lung transplantation) most CF sufferers died in adolescence or early adulthood. 

What is Fragile X Syndrome (FXS)?

In this day and age – because we can effectively screen for Down syndrome – FXS is the most common cause of inherited intellectual delay. People with FXS can have developmental delay, learning difficulties, anxiety, autism and epilepsy. The features of FXS can vary from mild to severe with boys more likely to be severely affected than girls. There is no cure for FXS although some interventions can improve outcomes for affected children.

What is Spinal Muscular Atrophy (SMA)?

SMA affects nerves in the spinal cord and causes muscles to get weaker with time. There are four types of SMA with Type 1 being the most common and the most severe. Babies with SMA Type 1 have weak muscles from birth and usually die before two years of age. There is no cure for SMA although some interventions can improve the quality of life of sufferers.

Please remember:

  • I recommend that you have testing for your carrier status for a number of conditions before your pregnancy if possible
  • These conditions are rare but devastating if they affect your child
  • You can be a carrier for these conditions without any problems yourself and without a family history of them
  • If you and / or your partner are carriers your baby may be
    • Affected by the condition, or
    • Unaffected by the condition, or
    • Another carrier for the condition (and unaffected themselves).
  • If we are aware of your carrier status we can offer relevant testing early on in your pregnancy although this is done via a “needle” test (a CVS or amnio) which carry a very small risk of causing a miscarriage
  • Unlike testing for, say, Down syndrome (which needs to be tested for in each pregnancy) these tests only need to be performed once in your life
  • With the best will in the world there are conditions we cannot test for – Cerebral Palsy and Autism are good examples – but it is worthwhile testing for the things we can test for (if you know what I mean).

I can organise these tests for you – all it involves is a simple blood test at one of the Douglass Hanly Moir labs.

The bad news:

These tests cost around $400. I don’t think Medicare chips in at all.

I have copied much of the information in this sheet from Sydney Ultrasound for Women’s brochure “Reproductive Genetic Carrier Screening” and the Victorian Clinical Genetics Services “Prepair Genetic Carrier Screening” information sheet. Its only plagiarism if I don’t cite my sources. As always I take full responsibility for any omissions or errors.