New scientific evidence dispute the beneficial effects of PGS / PGT-A in IVF treatment

Many fertility clinic websites claim that PGS can improve IVF success for older women and patients with multiple IVF failures or recurrent miscarriages. However, there has recently been increasing contradictory information from different sources, which dispute the beneficial claims of PGS in IVF treatment.

Here is a summary of new scientific evidence that dispute the beneficial effects of PGS / PGT-A in IVF treatment:

1) The biopsy procedure of PGS involve extracting and sampling cells from the outer embryo layer (Trophectoderm or TE) that gives rise to the placenta. This is not representative of the inner embryo layer (Inner Cell Mass, ICM) that goes on to form the actual embryo proper, which gives rise to the baby.

2) Mosaic embryos, which are embryos with a mixture of genetically normal (euploid) and abnormal cells (aneuploid) occur quite frequently and commonly among woman undergoing IVF (17% to 48%, please see link below). PGS often leads to the misdiagnosis and discarding of mosaic embryos, which have been shown to be capable of giving rise to a normal and healthy baby.

3) There is scientific evidence that Mosaic embryos are able to “self-correct”, which increases the chances of a normal birth. This “self-correction” mechanism involve pushing out the genetically abnormal (aneuploid) cells into the outer embryo layer (TE), which gives rise to the placenta.

4) Older women with low ovarian reserves have much fewer embryos during IVF. Therefore excluding or discarding of mosaic embryos that can potentially give rise to a normal baby, would in fact substantially reduce their chances of IVF success. Some older women may have no embryos left to transfer after PGS.

5) The PGS biopsy procedure of extracting cells from the embryo can potentially harm the embryo, and impair it’s development. Experts have pointed out that studies claiming no ill effects to embryos are often based on PGS of excellent-quality, healthy, robust embryos rather than more “delicate” embryos that might suffer more. If you have just one or two embryos, you might decide it is not worth the risk.

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Genetic testing of IVF embryos (PGS / PGT-A) – what Singaporean patients should know

Recently, Ms Rahayu Mahzam, Parliamentary Secretary of Ministry for Health — reported that the pilot trial of genetic testing of IVF (In Vitro Fertilization) embryos in Singapore suffers from a high attrition rate of 72% (2nd March 2021). She stressed the need to proceed carefully as there is some risk to the embryo during testing.

This procedure, also known as Preimplantation Genetic Screening (PGS) or Preimplantation Genetic Testing – Aneuploidy (PGT-A), involves screening the embryos of IVF patients whom are not known to be carriers of genetic diseases, unlike the closely-related Preimplantation Genetic Diagnosis (PGD) technique, which specifically tests for known genetic defects carried by prospective parents. Hence, the pertinent question that arises is why is there such a high attrition rate?

Yet at an earlier parliamentary session on 25th February 2021, MP Cheng Li Hui, called for less restrictions to make PGS (PGT-A) more widely available to IVF patients, on the basis that this procedure screens for the correct number of chromosomes to improve the chances of conception.

Hence, Singaporean IVF patients should be made aware of the widespread controversy and accumulating scientific evidence against the medical effectiveness of PGS (PGT-A) in improving the outcome of fertility treatment in patients, whom are non-carriers of genetic diseases.

Currently, PGS (PGT-A) is readily available to Singaporean patients at most foreign fertility clinics, particularly those from neighbouring countries. Indeed, many Singaporean patients who travel abroad for fertility treatment, often end up choosing to do genetic testing of their IVF embryos, not only for sex-selection, but also to eliminate the risks of Down Syndrome in older women and improve success rates.

This is due in large part to aggressive marketing of this technique by foreign fertility clinics, which substantially increases the costs of fertility treatment from 30% to 50%. Hence, it is imperative to highlight the controversial issues surrounding this expensive technique, which Singaporean patients and healthcare policymakers should be aware of.

Currently, there is good evidence that the PGS technique is fraught with false positive misdiagnoses due to the frequent occurrence of ‘mosaic’ embryos in IVF treatment. These are embryos that have a mixture of genetically abnormal and normal cells. Recent studies have shown that such ‘mosaic embryos’ can often give rise to healthy normal babies.

To understand why this is so, imagine the human embryo as containing multiple layers of cells, with the inner layers giving rise to the baby itself, while the outer layers give rise to the placenta and umbilical cord. Indeed, many studies of normal births often detect genetic abnormalities in the placenta and umbilical cord.

This is because nature has an amazing way of correcting genetic defects during the course of normal embryo development, by gradually pushing and segregating genetically abnormal cells to the outer layers that give rise to the placenta and umbilical cord, whilst preserving the genetic integrity of the inner layers that will eventually form the baby itself.

The problem with the PGS technique is that it only extract cells from the outer layers (Trophectoderm) for genetic testing, because sampling cells from the inner layers (Inner Cell Mass that forms the baby)
incurs too much risk of damaging the embryo. Hence the high incidence of false positive misdiagnoses associated with PGS, which often lead to discarding of ‘mosaic’ embryos, many of which can in fact give rise to a normal healthy baby.

Consequently, some studies have reported that PGS in fact reduces rather than improve the cumulative chances of IVF success. Because older women and women with low ovarian reserves usually produce less embryos during each IVF treatment cycle, the discarding of ‘mosaic’ embryos could in fact have a more devastating impact on their chances of success.

For such patients with very few available embryos, every single embryo (including mosaic ones) is more ‘valuable’, and would count more to their chances of reproductive success. Just recently in Australia, a class action lawsuit was launched by patients against Monash IVF for misdiagnosis by the PGS (PGT-A) technique, which led to discarding of their viable embryos that could have otherwise led to healthy births.

Although the PGS technique is often touted to be useful for avoiding birth defects such as Down syndrome in older women, patients must be aware that it is not a foolproof means of screening for genetic defects despite its high cost.

Usually, PGS screens only for a panel of common genetic defects, which excludes many rarer genetic diseases. It is also useless for detecting more complex genetic conditions that involve interaction of multiple genes with various factors within the birth environment, such as Autism Spectrum Disorders (ASD).

Patients should also be aware that the vast majority of genetically-abnormal embryos often fail to implant upon transfer to the womb during the IVF procedure; and even those genetically abnormal embryos that do implant often spontaneously abort at very early stages e.g. biochemical pregnancy.

Hence, patients should consider more economical means of screening for birth defects, such as the new generation of Non-Invasive Prenatal Testing (NIPT), that can screen for genetic defects in fetal DNA extracted from the pregnant mother’s blood sample.

Additionally, patients must also be wary of the aggressive sales pitch and marketing gimmicks routinely used to coax patients to undertake PGS during IVF treatment abroad.

One example is how the concept of relative risks is being misrepresented to patients, to play on their fears of birth defects. For example if the risk of Down syndrome is 0.1 % at age 20, and increases to 1% at age 40 and subsequently to 4% at age 45; then another way of presenting the data would be to say that the risk of Down syndrome increases 10-folds from age 20 to 40, and 40-folds from age 20 to 45.

Hence, through a sly manipulation of words and figures, the risks of genetic defects can be ‘exaggerated’ to patients who are unfamiliar with medical statistics.

Another dubious and ethically-questionable marketing tactic is to manipulate and play on the patient’s biased preference for either a boy or girl child, which may be helped by the fact that PGS is currently the most accurate and reliable embryo sex selection technique that is available in the market.

Last but not least, patients should also be aware of the risks of damaging the embryo during the ‘highly-delicate’ PGS procedure, which involves extracting cells from the embryo after drilling a hole through the embryo shell (Zona pellucida).

The smooth performance of this technique is often highly dependent on the skill and training of the laboratory staff (Embryologist). Even with high levels of training and accreditation, there is still a possibility of human error, particularly in a very busy laboratory that handles several such cases a day.

In conclusion, there is increasing scientific evidence that cast doubts on the medical benefits of PGS (PGT-A). There are certainly good reasons why the PGS technique is so stringently regulated by the MOH here in Singapore at the present moment, which is exercising due diligence to protect the welfare of patients.

Singaporean patients traveling abroad for IVF treatment should be cautious not to be ‘pushed’ into undertaking PGS unnecessarily, by asking themselves why this technique is so severely restricted in their own country, even if it is deemed to be so beneficial by profit-driven private fertility clinics abroad.


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