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Although both involve genetic testing, reproductive genetic carrier screening (RGCS) and preimplantation genetic testing (PGT) are different tests used at different stages for different purposes.
RGCS is a screening test, usually performed before pregnancy, to identify if you may have an increased chance of having a child with certain inherited genetic conditions. PGT is a test performed during IVF, after embryos have been created, to help identify embryos that are unaffected by a specific condition or, in some situations, to assess chromosomal status before transfer. They are not interchangeable, and they do not answer the same question.
RGCS is an optional genetic screening test that is usually offered before pregnancy, or sometimes in early pregnancy. It is relevant even if you are healthy and have no known family history of a genetic condition, because many people who carry a genetic variant do not know they are carriers. The purpose of RGCS is to identify people in the lower-risk general population who may benefit from further counselling and discussion of reproductive options if screening shows an increased reproductive risk.
RGCS is therefore different from targeted genetic testing. If there is a known family history of a specific genetic condition, or a known familial genetic variant, referral for genetics assessment and more specific testing may be more appropriate than screening alone.
RGCS is ideally performed during your family planning stage, before pregnancy, although it can also be undertaken in early pregnancy. Testing is usually performed on a saliva or blood sample. Different panels are available, ranging from smaller panels that screen for a few conditions to broader panels that cover many hundreds of inherited conditions.
Depending on the testing pathway used, screening may begin with one partner, with further testing of the other partner recommended if an increased reproductive risk is identified. Broader carrier screening panels are also available, which can be done for both partners at the same time.
If there is a known family history of a specific genetic condition, targeted genetic testing and genetic counselling may be more appropriate than carrier screening alone.
You can refer to Dr Huang’s list of some of the available RGCS tests, their comparison information, and how to access testing, which can be found here.
RGCS is usually performed on a saliva or blood sample. Depending on the laboratory, this may involve a home collection kit or collection at a pathology or clinic site.
Your sample is analysed for variants in the genes included in the selected screening panel. The purpose is to assess whether you are a carrier of certain inherited conditions that could be relevant when planning a pregnancy. Turnaround times vary depending on the test and laboratory used.
If screening identifies an increased reproductive risk, further counselling may be recommended to help you understand the result and discuss possible next steps. Depending on the situation, this may include partner testing, review by a genetic counsellor, or discussion of reproductive options such as natural conception, IVF with PGT in selected cases, or donor treatment.
PGT is a genetic test performed during IVF . It is not a population screening test. Instead, it is used in selected IVF situations, usually where there is a known increased genetic or chromosomal risk, or where embryo chromosomal assessment is being considered as part of IVF treatment. After embryos are created in the laboratory, a small number of cells are taken from the embryo for testing, and the result may help guide which embryos are considered suitable for transfer.
The key distinction is that RGCS identifies who may be at increased reproductive risk before pregnancy, while PGT tests embryos created during IVF. In selected situations, RGCS may identify a couple or individual as higher risk, and that information may then lead to discussion about whether IVF with PGT (specifically, PGT-M) is an appropriate option.
PGT may be considered in selected IVF situations, depending on the clinical context and the type of PGT being discussed. This can include if you have a known risk of passing on a specific single-gene condition or a known chromosomal structural rearrangement, and, in some cases, for those undergoing IVF where chromosomal assessment of embryos is being considered. The most appropriate option depends on your medical history, genetic history, fertility history, and the reason IVF is being undertaken.
There are three main types of preimplantation genetic testing:
PGT-A stands for preimplantation genetic testing for aneuploidy. It assesses embryos for chromosome number, looking for embryos with too many or too few chromosomes. Aneuploidy is one reason some embryos may not implant, may miscarry, or may result in certain chromosome conditions.
PGT-A is often recommended for:
PGT-M stands for preimplantation genetic testing for monogenic conditions. It is used when there is a known risk of passing on a specific single-gene condition, including autosomal dominant, autosomal recessive, X-linked, and some mitochondrial conditions.
Examples of conditions tested for include:
In this setting, PGT-M is performed during IVF to help identify embryos that are unaffected by the specific condition being tested for, so that suitable embryos can be considered for transfer.
This is the form of PGT most clearly linked to RGCS. If RGCS identifies that both partners carry variants associated with the same recessive condition, or otherwise identifies an increased reproductive risk, IVF with PGT-M may be one of the options discussed.
If you have already had a child with a monogenic condition, PGT-M could be a valuable way of ensuring your next child born through IVF does not have the same disorder.
PGT-SR stands for preimplantation genetic testing for structural rearrangements. It is used when one partner has a known chromosomal structural rearrangement, such as a balanced translocation or inversion. In these situations, PGT-SR may help identify embryos that have not inherited an unbalanced rearrangement and may therefore be more suitable for transfer. PGT-SR can minimise risk of miscarriage or severe abnormalities from unbalanced rearrangements in the baby.
PGT can only be performed if embryos have first been created through IVF. Eggs are collected, fertilised with sperm in the laboratory, and grown to the embryo stage.
Once embryos reach the appropriate stage, a small number of cells are removed for genetic testing. The results may help guide which embryos are considered suitable for transfer, depending on the type of PGT being performed.
Depending on the result, embryos that are unaffected by the specific condition being tested for, or that have the chromosomal result considered appropriate in that context, may be considered for transfer. The decision about embryo transfer is made in the context of the full clinical picture rather than on a genetic result alone.
PGT is highly specialised, but no test is perfect. Because only a small number of cells are tested, results can occasionally be inconclusive or may not fully reflect the entire embryo. This is one reason why routine testing in pregnancy is still recommended.
No, PGT is optional and is not recommended for everyone having IVF. It is usually considered only in selected situations, such as known genetic risk, a chromosomal rearrangement, or when embryo chromosomal assessment is being discussed as part of IVF treatment planning.
If an embryo is found to be unsuitable for transfer based on the type of PGT performed, the available options will be discussed with you. Depending on the result, consent arrangements, and clinic policy, embryos may be stored, discarded with consent, or in some circumstances donated for approved research.
PGT does not guarantee pregnancy or create healthy embryos. Its role is to provide additional genetic information about embryos created during IVF, which may help guide embryo selection in selected situations. This may decrease time to a successful pregnancy and decrease miscarriages.
In some situations, PGT may be discussed where embryo chromosomal abnormalities are thought to be contributing to miscarriage or repeated unsuccessful IVF treatment. Whether it is likely to help depends on your individual circumstances and the type of PGT being considered.
No, PGT only tests for the specific condition or chromosomal issue it has been designed to assess. A normal PGT result does not rule out every possible genetic, developmental, or pregnancy-related problem.
No, PGT is performed on embryos during IVF before transfer. Prenatal testing is performed after pregnancy has been established and it is still recommended even if PGT has been used.
PGT usually adds extra steps to IVF, including embryo biopsy, genetic analysis, and waiting for results. In many cases, this means embryo transfer takes place in the following month at a later cycle rather than immediately.
PGT may be considered for selected IVF patients, including those with a known genetic condition, a chromosomal rearrangement, recurrent pregnancy loss, or repeated unsuccessful fertility treatment. The most appropriate option depends on your medical, genetic, and fertility history.
Collaborating with the world-class technology and innovative research of fertility network Genea, Dr Alice Huang offers comprehensive fertility care for individuals and couples at all stages of their family-building journey.
Her Melbourne fertility clinic is easily accessible at Epworth Freemasons Hospital in East Melbourne.
Contact Dr Huang’s rooms today to take your first step towards parenthood.
