Undertaking Preimplantation Genetic Diagnosis

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You can undergo several tests when you're pregnant to make sure that the foetus has the right number of chromosomes and, if you're at risk of passing on a severe genetic condition, that the foetus is unaffected by this condition. However, although this is all well and good if the test results come back normal, if the results reveal a problem with the foetus, you then have to make the heart-wrenching decision whether to terminate the pregnancy or continue knowing that your baby has a potentially severe health problem.

To avoid this dilemma, you can opt for your embryos to be tested in the lab before you fall pregnant. To do this, you undergo an IVF treatment cycle (I explain the cycle in Chapter 5) and then have the resultant embryos tested, to make sure that only those that aren't affected by the condition tested for and have the right number of chromosomes are transferred. This is called pre-implantation genetic diagnosis — or PGD for short.

Some people oppose testing of embryos and argue that it can lead to 'designer babies', whereby embryos are selected based on whether they have certain desirable genes such as an athletic gene or an academic gene. However, athletic or academic talent doesn't come from a single gene and not only that — such talent very much depends on the environment in which the child grows up. So PGD can't actually be used to make 'designer babies'.



Testing for severe genetic conditions

Some genetic conditions cause extreme and lifelong suffering. These include

1 Beta-thalassaemia: This blood disorder leads to a lack of oxygen in many parts of the body and anaemia, which can cause weakness, fatigue and more serious complications.

1 Cystic fibrosis: This life-threatening genetic disorder predominantly affects the lungs and digestive system. People with cystic fibrosis produce an abnormal amount of thick mucus that blocks the airways, leading to repeated lung infections.

1 Fragile X: This genetic disorder results in a range of physical, intellectual, emotional and behavioural problems.

1 Huntington's disease: This genetic disorder affects muscle coordination and some cognitive functions.

1 Spinal muscular atrophy: This genetic disorder results in progressive muscle wasting and weakness.

Scientists have discovered exactly where the faulty genes that are responsible for these severe conditions are located, so now highly specialised embryologists can use PGD to test embryos to find out whether they're affected by these disorders or not.

Some genetic conditions, such as haemophilia and Duchenne muscular dystrophy, affect only boys, not girls. If you have a known risk for one of these so called X-linked diseases, embryologists can determine the sex of your embryos and transfer only 'girl' embryos. However, sex selection for so-called family balancing reasons — where a female (or male) embryo is chosen because the parents specifically want a girl (or boy) — can't be carried out in Australia: In 2005 the Australian Health Ethics Committee ruled that embryo sex selection is permissible for medical reasons only.

Using PGD for other reasons

If you have numerous good-quality embryos transferred without success or you miscarry several times, your embryos may be aneuploid, meaning that they have the wrong number of chromosomes. If your doctor thinks that this may be the case and your clinic performs PGD, you may be offered the procedure to see whether you have a high number of aneuploid embryos and to ensure that aneuploid embryos aren't transferred.

If you've experienced several miscarriages, your doctor may suggest that you and your partner have a blood test to determine whether the miscarriages were the result of a balanced translocation (where a piece of chromosome breaks off and attaches to another chromosome). People with a balanced translocation don't normally have health problems as a result of the translocation because they have the full complement of genetic material — but their sperm or eggs may have some missing or extra genetic material, which can lead to miscarriage. If your miscarriages were the result of a balanced translocation, your doctor may suggest that you opt for PGD of your embryos to check that the embryos have the correct amount of genetic material before being transferred.

Performing PGD

PGD is performed at the bigger IVF clinics only, because the procedure requires extremely sophisticated lab equipment and specially trained and very skilled embryologists. If you have a known or suspected genetic condition and your doctor thinks PGD can be used to avoid passing this condition to your baby, you and your partner follow these steps:

1. Undergo a genetic test: To check whether one or both of you carry the 'faulty' gene or have a balanced translocation, you have a blood test or buccal swab (whereby cells are collected by swabbing the inside of your cheek).

2. Have a consultation with a geneticist or genetic counsellor: At this meeting the geneticist discusses the results of your genetic tests and advises whether PDG is feasible in your situation.

3. Meet with your IVF doctor: Your doctor explains what PGD involves and outlines the pros and cons of the procedure.

If you decide to go ahead with PDG, you undergo an IVF treatment cycle up to and including embryo development in the lab (refer to Chapter 5), so that ideally several embryos are available for testing. The PGD process then proceeds as follows:

1. The embryologist performs embryo biopsy: Three days after egg retrieval, when the developing embryos have about eight cells each, the embryologist removes one or two cells from all the embryos that have developed for testing.

Note: Some clinics wait until five days after egg retrieval so that they can remove several cells from each embryo.

2. The embryologist carries out genetic testing on the chosen cells:

• If your embryos are being tested for a genetic condition, the embryologist determines whether the faulty gene is present or not in each cell.

• If your embryos are being tested for the right number of chromosomes, the embryologist verifies that the cells have the correct number (two) of the eight chromosomes that can be tested.

If PGD reveals healthy embryos, on day five after egg retrieval you have one or two embryos transferred. Additional healthy embryos can be frozen (see Chapter 5 for more information on freezing your embryos). After a couple of weeks of crossing all your fingers and toes, you have a pregnancy test, which hopefully comes back positive!

Understanding the (imitations of PGD

The fact that some cells are removed from the early embryo in the PGD procedure doesn't appear to have any negative effects on either the embryo's chance to implant and develop or the health of the resultant baby. However, you need to be aware of the following before you agree to PGD:

i If you're having PGD to check which of your embryos has the right number of chromosomes but have only one or two embryos available, your doctor may advise you not to go ahead with the procedure. This is because it's more beneficial to transfer these embryos without subjecting them to biopsy.

i If you're having PGD because you risk passing on a genetic condition and want to be sure that the baby is unaffected, PGD may be done even with a small number of embryos.

i Only good-quality embryos can be tested, so if on day three your embryos haven't developed to the eight-cell stage or have a lot of fragments (refer to Chapter 7 where I explain more about good-quality embryos and what constitutes poor quality), PGD can't be carried out.

i Test results can be incorrect or inconclusive. For example, embryos can have a mixture of normal and abnormal cells, so even if the few cells that are tested are okay, the rest of the embryo may not be. And occasionally, PGD results aren't as clear as desired and can be difficult to interpret.

i The fact that PGD shows that an embryo is free of a certain disease doesn't guarantee that the embryo is free of other genetic conditions.

^ Very rarely, an embryo is damaged during the embryo biopsy procedure and stops growing, so it cannot be used.

^ To verify the PGD result, clinics recommend that you have prenatal diagnosis if you become pregnant after PGD. This is because the accuracy of prenatal testing results is higher the more cells that are tested. With PGD, only one or two cells are tested, whereas with chorionic villus sampling and amniocentesis thousands of foetal cells are tested and these procedures have 99 per cent accuracy.


Your doctor advises you not to have unprotected sex during the cycle in which your embryos undergo PGD, in order to eliminate the risk that you conceive spontaneously and have a foetus with a genetic or chromosomal defect.

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