Preimplantation genetic testing for aneuploidy (PGT-A) is a test to screen embryos, which have been made in an IVF cycle, for chromosomal abnormalities. Generally speaking, embryos identified as having chromosomal abnormalities are considered abnormal or aneuploid and are not recommended for transfer. If no abnormality is detected, the embryo is presumed to be normal or euploid. In this way, PGT-A results are used to decide which embryos should or shouldn\u2019t be transferred. PGT-A is sometimes referred to by its old name, \u2018PGS\u2019 (\u2018S\u2019 for screening).<\/p>\n\n\n\n
Chromosomal abnormalities are the most common cause of IVF failure, and their incidence increases dramatically with female age, assuming women are using their own eggs.<\/p>\n\n\n\n
PGT-A is a controversial test, which the Human Fertilisation and Embryology Authority (HFEA), the UK\u2019s fertility regulator, has classified as an \u2018add-on\u2019. This means that they don\u2019t believe there is sufficient evidence yet to justify its routine use for most patients in IVF. The key word here is \u2018routine\u2019 \u2013 the HFEA do not currently provide a position on whether PGT-A may benefit some patients – for example, older women (1).<\/p>\n\n\n\n
Let\u2019s start with what PGT-A cannot do. It cannot improve embryo quality, detect specific genetic changes (for example those causing genetic disease such as thalassemia) or increase chances of success if all of your embryos will eventually be transferred anyway (so-called cumulative pregnancy or cumulative live-birth rate).<\/p>\n\n\n\n
However, there is evidence that as a selection tool, PGT-A can reduce the chances of miscarriage, support the use of single embryo transfer and reduce the time to pregnancy (by transferring the \u2018normal\u2019 embryos sooner), thus potentially saving you time, money and heartache.<\/p>\n\n\n\n
Your embryos are grown in the usual way until around day 5 or 6 (the blastocyst stage) when a small number of cells (between 5 and 10) are removed from the embryo (a technique known as embryo biopsy) for analysis. Meanwhile the remaining embryo is vitrified (frozen) and stored for later use in a frozen embryo transfer cycle (FET). The biopsied cells are sent to a testing laboratory that generally uses DNA sequencing technology to identify the average number of chromosomes present in the sample. While the technology itself is very accurate, it is important to understand that the cells biopsied are only an approximation of the whole embryo \u2013 PGT-A analyses 5-10 cells from a blastocyst containing around 100 cells, and there is a chance that the cells analysed may not be representative of the whole embryo. Most advanced PGT-A tests available today deliver very similar results and, in my experience, how the clinic and testing laboratory work together can have more impact on the quality of the results than small differences in technology.<\/p>\n\n\n\n
The best evidence suggests that patients most likely to benefit from PGT-A are those of advanced maternal age (usually defined as >35 years). Other reasons for testing include patients with a history of poor outcomes such as miscarriage, severe male factor infertility and repeated IVF failure \u2013 while the evidence is less robust for these categories than for advanced maternal age, some patients may benefit. If you are considering PGT-A, or if your clinician has suggested PGT-A, it is important that you understand how the test is relevant for you and the reason for performing the testing.<\/p>\n\n\n\n
\nThere are a lot of studies on PGT-A that show us that PGT-A can be useful. One of the studies from Igenomix says that women between the ages of 38 and 40 years old undergoing IVF treatment have a 64% chance of having aneuploid embryos. Then the rate of aneuploid embryos increases as the maternal age increases.<\/p>\nSofia Rodrigues, clinical embryologist at Ferticentro<\/a><\/cite><\/blockquote>\n\n\n\n
What are the risks?<\/h2>\n\n\n\n
There are no risks to you directly as a patient (other than those present for IVF in general). However, there is a risk that you may have fewer or no embryos available for transfer if some or all embryos are reported as abnormal. If these embryos were incorrectly reported as abnormal (false positives) there is a chance that you would discard a potentially normal embryo. In recent years, the widespread reporting of mosaicism (a situation in which the sample appears to consist of a mixture of normal and abnormal cells) may have led to an increase in false positives. However, with better understanding, new clinical evidence and the support of genetic counsellors, the chance of discarding \u2018normal\u2019 embryos has dramatically reduced to around 2%.
As with any laboratory procedure, there is also a small chance that your embryo could be damaged during the biopsy, but this risk varies according to the skill and experience of the embryologist. There is also a small chance that the lab provides no result for one or more of your embryos. This is usually because the cells taken from the embryo were not successfully detected in the sample provided to the genetics lab \u2013 the incidence of this is generally between 1-3%. Some clinics perform a second biopsy (a \u2018rebiopsy\u2019) on no-result embryos, or they may provide guidance on whether to consider transferring an embryo with no result.<\/p>\n\n\n\nWho pays for PGT-A and what are the costs?<\/h2>\n\n\n\n
PGT-A is not currently NHS-funded, and it may not be possible to add this treatment to your NHS-funded IVF cycle, even if you are prepared to pay for it yourself. In the UK, private clinics may charge for PGT-A in different ways: <\/p>\n\n\n\n
(a) a fixed amount for an \u2018average\u2019 number of embryos tested. Typically, this can be between \u00a32500-\u00a34500 per round of testing; or <\/p>\n\n\n\n
(b) a fixed biopsy fee plus a fee per embryo tested. There is a wide variation in the pricing models and the actual prices charged between clinics. It is important you establish this pricing up front to avoid any unwelcome surprises.<\/p>\n\n\n\n