Preimplantation genetic testing (PGT) is a specialised form of IVF that allows us to screen embryos for certain genetic conditions before pregnancy.
PGT is one of the reproductive options available for individuals and couples with a high chance of having a pregnancy with a genetic condition.
In most cases the other reproductive options include:
Accepting the chance and considering diagnosis later in life
Natural conception and testing during pregnancy (prenatal diagnosis)
Assisted reproduction using donated eggs, sperm or embryos
Adoption, fostering or other forms of parenting
Deciding not to have children or any further children
What are the types of PGT?
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PGT-M – Testing for a monogenic condition
If you or your partner have a high chance of a pregnancy with a single gene condition, for example, cystic fibrosis, hereditary breast/ovarian cancer (BRCA1/BRCA2), Huntington’s Disease.
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PGT-SR – Testing for a structural rearrangement
If you or your partner have a chromosome translocation linked to infertility, miscarriage, or chromosomal conditions. Carriers of Robertsonian or reciprocal translocations may benefit from PGT-SR.
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PGT-A – Testing for aneuploidy (chromosomes)
If you want to reduce miscarriage risk by selecting embryos with the typical number of chromosomes. This form of PGT is typically used by people undergoing IVF for fertility reasons.
In principle, it should be possible to design a test for any genetic change which has been identified in an egg or sperm provider, and in most cases genetic changes which have been identified in a previous pregnancy (de novo changes). All forms of PGT include an assessment of chromosomes (PGT-A) and can test for multiple genetic conditions in the one test. It is also possible to use PGT for:
Medical sex selection – When a condition affects one sex more severely, but a genetic test is not available to identify embryos at a higher chance (e.g. autism spectrum disorder).
HLA matching – When a child could benefit from bone marrow transplantation and requires umbilical stem cells or bone marrow cells from a sibling with the same immune profile.
Blood group incompatibility – When there is a chance of haemolytic disease of the fetus and newborn or fetal and neonatal alloimmune thrombocytopenia.
Exclusion testing – When there is a strong family history of a dominant condition (e.g. Huntington’s disease) but the status of the individual is not known.
We will review your personal and family history and arrange tests to give you more information about your chances of success with IVF treatment with PGT.
Genetics Review – We will review your genetic test results, discuss your reproductive options, explain what PGT can (and can’t) achieve, and confirm that PGT is a suitable option for your situation.
Fertility Review – We will review your obstetric, gynaecological and fertility history, and arrange tests to understand your chances of success with IVF.
How do I start the process?
What tests do I need to do before having IVF treatment with PGT?
If you decide that you would like to go ahead with IVF and PGT, we will undertake a PGT test design by collecting DNA samples from you, your partner, and sometimes other family members. Using DNA fingerprinting, we design a personalised test that can detect the genetic changes of concern, check for chromosomal issues, and reduce the risk of inconclusive results.
It is possible to undertake an IVF cycle to generate embryos while awaiting the test results from PGT test design and other investigations. In rare cases we will not be able to design a test using standard methods and this may result in delays in results from embryo testing or an inability to provide a result on the embryos generated.
Before starting IVF, we also arrange tests to help your cycle go smoothly:
Hormone testing & ultrasound (to predict ovarian response and choose medication doses).
Semen analysis (to ensure sperm quality for fertilisation).
Carrier screening & karyotype testing (to detect other conditions that may need to be added to the PGT design).
Infection screening (to ensure safe treatment).
What are the main factors which determine success in IVF?
The main factors which determine success in IVF are the age of the egg provider and expected number of eggs from a treatment cycle (ovarian reserve). The ovarian reserve can be assessed using an AMH level and a pelvic ultrasound to identify the number of follicles likely to be available in an average cycle (antral follicle count).
Other fertility factors and pregnancy history can have an influence on the chances of treatment success. We tend to consider treatment success over multiple stimulated IVF cycles and can compare your chances to other people in your situation using online databases.
What does an IVF cycle involve?
An IVF cycle typically involves:
Taking hormone injections to support egg development for ~2 weeks, with blood tests and ultrasounds to track progress
A procedure to remove the eggs from the ovaries under light anaesthetic (egg pick up)
Fertilising eggs with individual sperm in the lab (ICSI)
Growing embryos for 5-7 days until they are ready to have a few cells removed (embryo biopsy)
Freezing any embryos which have been biopsied while testing takes place
In any IVF treatment cycle there is a chance that there are no embryos suitable for testing or no embryos suitable for transfer. This may be because the ovarian stimulation does not result in the development of enough follicles to proceed to egg pick up (poor response), no eggs are retrieved during the egg pick up (premature ovulation, empty follicles), inadequate sperm to proceed to fertilisation, failed fertilisation or egg breakdown following ICSI, or failed embryo development.
What are the medications used in an IVF cycle?
The medications used in an IVF cycle are injected under the skin (subcutaneous injection) on a daily basis starting on Day 2 of the treatment cycle.
Follicle stimulating hormone (FSH) is taken to support the growth of the follicles that are present in the monthly cycle. This medication is taken from day 2 of the treatment cycle for approximately 8-12 days. Examples of trade names include Gonal F, Menopur, and Elonva (long-acting FSH).
A GnRH antagonist (e.g. Orgalutran/Ganarelix, Cetrotide) is taken from day 6 of the treatment cycle until the time of the trigger injection to prevent premature ovulation of the follicles that are developing.
A trigger injection (e.g. Ovidrel, Lupron) is taken once sufficient follicles have developed to proceed to egg pick up, allowing the eggs to mature and prepare for fertilisation in the laboratory. This medication is prescribed at a specific time, usually 36 hours prior to the planned egg pick up.
What are the risks of taking IVF medications?
In each IVF cycle the aim is to support a sufficient number of follicles (10-15) to maximise the chance of having embryos for testing. It is possible that the medication will fail to achieve a sufficient response (poor ovarian response) or will cause an over-response (ovarian hyperstimulation syndrome).
Poor ovarian response is more common when there is low ovarian reserve as indicated by a low AMH and low follicle number on ultrasound prior to treatment but can occur in any treatment cycle. There may be no eggs or few eggs obtained at egg pick up, or cancellation of the cycle prior to egg pick up if there are not sufficient follicles developing. Adjustment of the dose or changing the stimulation protocol may result in a different response in subsequent cycles, noting there is natural month-to-month variability in ovarian response even at the same dose of medication.
Ovarian hyperstimulation syndrome (OHSS) is more common when there is high ovarian reserve, young age and/or polycystic ovaries on ultrasound prior to treatment but can occur in any treatment cycle. OHSS causes fluid to leak from blood vessels which can lead to severe abdominal bloating (ascites) and difficulty breathing due to fluid around the lungs (pleural effusion). Severe cases can cause kidney and liver damage, blood clots (DVT) which can travel to the lungs (PE), requiring hospital admission and intensive care. Treatment is supportive and OHSS will usually resolve with the assistance of cycle modification and additional medications. The risk of severe OHSS is low in PGT cycles (<1%) because embryo testing requires a freeze all protocol and transfer in a frozen embryo transfer cycle, where there is little or no risk of OHSS.
Minor side effects of medications such as bruising or discomfort at the injection site are common, as are bloating and pelvic discomfort due to enlargement of the ovaries. Less common side effects include fatigue, headaches, weight gain, mood swings, nausea, and in rare cases allergic reactions to medication. There is no evidence of long-term side effects of the use of fertility drugs, including no evidence of an increased chance of cancer.
What does an egg pick up involve?
Transvaginal oocyte retrieval or egg pick up is performed usually around 2 weeks following the commencement of medications. You are required to have an empty stomach (i.e. fast from midnight before the procedure) and will have a general anaesthesia for 10-30 minutes to reduce discomfort during the procedure.
A transvaginal ultrasound probe is used to guide a needle into each ovary and drain the fluid which is present in the follicles within the ovaries. As each follicle is drained, the fluid is examined by an embryologist in theatre under a microscope to identify the eggs.
At the conclusion of the procedure, you will wake up in recovery and be informed of the number of eggs collected. Later in the day will be informed of the number of eggs which have been injected with sperm (ICSI).
You will not be able to drive yourself home following the procedure and may have some abdominal pain or vaginal spotting for up to 24 hours.
Very rarely, an egg pick up may result in more significant complications:
Pelvic infection due to transfer of vaginal bacteria into the abdominal cavity, requiring oral or intravenous antibiotics and in rare cases hospitalisation or surgery
Significant bleeding from the vaginal wall or ovaries due to damage to blood vessels, resulting in surgery, loss of the ovary or blood transfusion
Damage to organs such as the bowel, bladder, uterus and ovary from the procedure resulting in the need for additional surgery
Anaesthetic reactions requiring additional hospitalisation and treatment
What happens to my embryos in the lab?
Following egg pick up, mature eggs are identified by the embryology team and the surrounding cells removed prior to injection with individual sperm (ICSI). By removing the additional cells around the egg and using individual sperm, the risk of DNA contamination is minimised.
Injection of a sperm into an egg does not guarantee fertilisation, which is a biological process. The eggs which have been injected are visualised the next day to confirm the presence of two pronuclei representing the genetic material from the sperm and egg to identify how many eggs have fertilised. Atypical fertilisation refers to eggs which appear to have 0, 1, or 3 or more pronuclei. These embryos are cultured and can be tested as part of the PGT process to confirm whether there are additional or missing sets of genetic information.
Fertilised eggs are supported in fluid which contains the nutrients required for early embryo development (culture medium) and pass through different stages of development throughout the week.
Day 1: Zygote (1 cell)
Day 2: Early Embryo (2-4 cells)
Day 3: Cleavage stage (4-8 cells)
Day 4: Morula stage (16-32 cells)
Day 5-7: Blastocyst stage (100-200 cells)
At each stage, it is expected that a proportion of embryos will stop developing, usually resulting from chromosome errors in the early cell divisions. Overall, 20-30% of fertilised eggs may be expected to reach the blastocyst stage and be considered for embryo biopsy. The average number of embryos biopsied in a PGT cycle ranges from 2-4 depending on the age of the egg provider.
During an embryo biopsy, a small number of cells (5-10) are removed from the outside layer of the embryo which goes on to form the placenta, avoiding the inner cell mass which goes on to form the baby. There is a small risk of loss of the embryo during the procedure.
Embryos which are biopsied are frozen (vitrified) while the sample is sent to the laboratory to amplify the DNA and perform the test which has been designed for your cycle. Embryo survival following freezing is very high (96-98%), which means there is a small possibility that an embryo will not be viable when it is thawed for a later transfer. The pregnancy and child health outcomes from embryos which have been biopsied and frozen are expected to be comparable to the normal population.
What results can I get from my PGT cycle?
PGT will generally report embryos as suitable for transfer or not suitable for transfer based on the condition being tested. In general terms the results will usually be reported as:
High Risk: The embryo has a high chance of the specific genetic condition and/or chromosomal abnormality. These embryos are not suitable for transfer.
Low Risk: The embryo has a low chance of the condition and the expected number of chromosomes. These embryos are suitable for transfer. A low-risk result reduces but does not eliminate the chance of a genetic or chromosomal condition.
Intermediate Risk: The embryo has a high chance of a genetic change that may result in variable impacts on the health of a pregnancy or child, including but not limited to mosaicism (where a chromosome error is in some, but not all, the cells of an embryo), sex chromosome changes and female embryos with variants in X-linked conditions. These embryos may be suitable for transfer following further consultation.
No Result: The sample was insufficient for testing. A repeat biopsy may be required to obtain a result. This may occur for some or all embryos in a cycle.
PGT is highly accurate but not 100%. A low-risk result reduces but does not exclude the chance of the condition. Prenatal diagnostic testing is recommended for confirmation in an ongoing pregnancy following PGT.
Natural conception can occur during treatment cycles. Unprotected intercourse should be avoided during IVF and FET cycles.
In rare cases, test design may not be possible and PGT cannot proceed. Incidental findings or unexpected relationships are not reported unless relevant to test design. It is recommended to await test design completion before starting IVF.
There is a small risk of damage or unsuitability for biopsy or freezing. Embryo biopsy and freezing do not appear to have an impact on the health of a pregnancy or child following PGT.
Biopsied cells or amplified DNA may be transported between IVF centres or laboratories for testing. Samples are handled under strict conditions by trained staff or couriers. Despite all precautions, loss or damage may occur.
PGT cannot guarantee that a baby will be free from all abnormalities. Every pregnancy carries a background 3–5% risk of birth defects or genetic conditions. PGT detects only the specific changes outlined in the test design and chromosomal aneuploidy, not other unrelated risks.
What are the limitations of PGT?
What does an embryo transfer involve?
You will receive your results from the genetics laboratory approximately 4 weeks after embryo biopsy. If you have embryos which are suitable for transfer, they can be transferred in a frozen embryo transfer cycle. In most cases, this will involve tracking your hormone levels using blood tests to identify when ovulation occurs. Embryo transfer is timed following ovulation to mimic when a naturally conceived embryo would implant in the lining of the womb.
Embryos which are suitable for transfer are thawed on the day of transfer and placed in the uterine cavity with a thin plastic tube (catheter) under ultrasound guidance.
A single embryo is transferred to reduce the chance of multiple pregnancy. Identical (monozygotic) twins or higher order multiple pregnancies (triplets, quadruplets) can still occur due to splitting of the embryo after transfer. This occurs 1-2% of the time which is higher than the background rate in naturally conceived pregnancies). Tubal (ectopic) pregnancy can occur in an IVF cycle despite placement in the uterine cavity.
The overall success of each embryo transfer following PGT is approximately 50%. If you are not pregnant following embryo transfer and have additional low risk embryos for transfer, you can book on for your next frozen embryo transfer cycle straight away. If you do not have any further embryos suitable for transfer, you can book on for an IVF cycle to generate more embryos or seek additional review before making decisions about next steps.
What do I do once I am pregnant following PGT?
Pregnancy is confirmed using blood tests following embryo transfer and an ultrasound is booked at around 7 weeks from the date of the last menstrual period to confirm the location and number of ongoing pregnancies.
You will be offered prenatal diagnostic testing by chorionic villous sampling (CVS) at 11 weeks of pregnancy or amniocentesis at 15 weeks of pregnancy in any pregnancy following PGT to confirm the result. If you choose not to have prenatal diagnostic testing, other routine screening options including prenatal cfDNA screening (NIPT) will be arranged by your obstetric provider.
Pregnancies following IVF with PGT may have a slightly higher risk of birth defects compared to the general population, although in other respects they may have a lower risk of certain genetic conditions (following expanded carrier screening and chromosome screening which is routinely performed prior to PGT). With the exception of multiple pregnancy, IVF pregnancies are not considered high risk outside of other obstetric factors and routine obstetric care is recommended.
Embryos with a high-risk result are generally not suitable for transfer under NHMRC Guidelines. These embryos will be disposed by embryology teams at routine intervals according to local practice.
If you wish to consider storage or transfer of a high-risk embryo, additional fees, consultation and consent may be required. It is possible that these embryos will not be available for transfer even following these processes.
What happens to embryos with a high-risk result?
What do I do if I have further questions?
Please do not hesitate to contact us if you have questions about PGT that have not been covered in this treatment guide.
PGT is constantly changing and we are happy to provide advice about the latest options.