A genetic test, known as pre-implantation genetic screening (PGS), is widely used to get better results in IVF. A large majority of IVF failures are blamed on poor embryo quality and fertility experts recommend PGS to be able to select the best embryo that is most likely to result in a positive pregnancy. So how does PGS improve IVF success rates?
Using PGS, the embryos can be checked for abnormal chromosome number (aneuploidy), which is a major cause of both implantation failure and miscarriage. This allows the doctor to transfer only healthy embryos into the uterus, thus improving the chances of IVF success.
PGS is also known as pre-implantation genetic testing for an aneuploidy (PGT-A).
PGS and IVF success
Chromosomal abnormalities in embryos are common. In fact, according to a study published in Biomed Central, nearly 50% of all IVF embryos are actually aneuploid.
Dr. Tan, from one of Asia’s top IVF clinics for genetic testing, explains in the below video how PGS helps improve IVF success:
However, there are certain scenarios in which the chances of having abnormal chromosome number are higher. For this reason, there are certain patient groups who may stand to benefit from PGS more than others.
When is genetic testing of embryos required?
- If one or both partners are carriers of a genetic disorder, PGD will be recommended
- Women who have had several failed fertility treatments
- Women who have experienced recurrent miscarriages, including ‘chemical’ pregnancies.
- Women who are over the age of 35 and hence at a greater risk for aneuploidy
Recurrent miscarriages and failed IVF cycles can be the result of aneuploid embryos. The incidence of chromosomal abnormalities and consequent fertility problems increases with advancing maternal age, and by employing PGS technology, the transfer of aneuploid embryos can be avoided. With the transfer of healthier embryos to the uterus, you have better chances of IVF success.
PGS can increase the rate of clinical pregnancy
PGS enhances the success of IVF but not in all cases; the success rates vary by age.
The chart below, based on information published in Reproductive Biomedicine Online, in 2016, shows:
- There is much better chance of IVF success with PGS testing in women who were over the age of 35. The largest increase in rates occurred in women aged between 38 and 41.
- PGS had very little impact on the rate of pregnancy in women below 35.
Taking into account the effects of increasing age on fertility, these results are not surprising. They suggest that women in their late 30s are more likely to benefit from PGS and that there may be very little benefit in the use of PGS to improve IVF success rates in women under 35.
To add weight to this data, another study published in Fertility and Sterility, in 2013 found that:
If a chromosomally normal embryo is transferred into an older woman, the chances of successful implantation and pregnancy are not significantly different to that of a younger woman.
Additional studies and data from fertility clinics also support these findings. As an example, the Biomed Central study mentioned above states that IVF success rate with PGS tested embryos was 69.1 percent as compared to 41.7 percent in cases where the embryos were selected simply based on their morphology.
Embryos that look healthy on examination under the microscope can still have potential problems that may affect successful implantation and pregnancy. IVF success rates with chromosomally normal embryos are significantly higher than those with non-genetically-tested embryos.
What are the other benefits of PGS?
Besides enhancing the rates of successful clinical pregnancies from IVF, genetic testing also has several other benefits as:
Reduced risk of miscarriage:
Single miscarriages are relatively common, with 1 in 4 pregnancies ending this way. Multiple miscarriages however are less common and can be caused by chromosomal abnormalities. Therefore, choosing only the healthiest embryos for transfer may help to prevent this.Despite there being limited data available, a systematic review published in Fertility and Sterility in 2011, describes a marked decrease in miscarriage rate from 28% in the natural conception group, to 9% in the PGS group.
Reduced risk of multiple pregnancies:
Since PGS tested embryos have better success rates, the doctors don’t need to take their chances with multiple embryo transfers, which may result in dangerous outcomes for both the mother and the baby. Dr. Colin Lee, who has extensive research and authority in the subject, and his associates have been able to demonstrate an average clinical pregnancy rate of 82.9 percent from the transfer of a single good graded euploid blastocyst.- Speed up successful IVF process:
PGS may shorten the length of time needed to achieve a successful pregnancy. This can be a particularly important factor, given how emotionally and financially draining the process of IVF treatment can be. Reduced financial burden: Even though PGS is an added expense in your IVF treatment, it can actually save you money by helping achieve the pregnancy without wasting extra money for subsequent frozen embryo transfers or repeat cycles.
Limitations of PGS testing in IVF
Given that only about 70% of PGS embryos lead to a healthy pregnancy, there must be some limitations to the genetic testing procedure. These include:
- Limited sample size: Only a few cells from the outer section are removed for PGS analysis, leaving intact the inner cells that will actually give rise to the baby. It was believed that the limited sample may not accurately represent all cells within the embryo. However, scientific research has shown that the outer portion of the embryos is similar to the inner and there is a significant connection between the two. Therefore, the biopsy sample taken is representative of the entire embryo.
- Mosaicism: Mosaic embryos have both normal and abnormal cells. If the number of abnormal cells is small, these embryos may still be healthy and their use may or may not result in a healthy pregnancy.
- Invasive procedure: There were concerns regarding possible damage to the embryo by taking cells from it at such an early stage of development, so the doctor’s advise against biopsy on Day 3. Performing the biopsy at day-5 blastocyst stage keeps embryo viability intact.
- Difficult decision: Besides the financial aspect, it is sometimes an emotionally difficult decision for parents to have their embryos biopsied. Professional and psychological support from the doctors is helpful in this situation.
- No viable embryos in the cycle: Women of advanced age sometimes have very few embryos in an IVF cycle, and PGS testing may find that none of them are viable. Even though it is better than having a chromosomally abnormal (aneuploid) embryo transferred but to the patient it may feel like a wasted cycle without any transfers.
Do you need Genetic Testing with IVF?
PGT-A is usually recommended by fertility doctors to the patient groups described above; it is not for everyone.
Aneuploid embryos may lead to failure in establishing and maintaining a successful pregnancy. If there is an indication of the possibility of having chromosomal abnormalities in your situation, the doctor/embryologist will guide you regarding PGT-A.
Studies and clinical data show an increase in pregnancy rates when genetic testing is combined with IVF. As shown in the data from Reproductive Biomedicine Online presented above, this increase can be as much as 30 percent.
Besides increasing the chances of a positive pregnancy, genetic testing of embryos reduces the chances of miscarriage and raises significantly your possibility of delivering a healthy baby.
For more information and cost of PGS with IVF, get in touch via the form on this page. For any questions/comments, write in the section below.
Authored with contributions from Dr. Tan Chong Seong, Obs, Gyne and infertility expert.
Resources:
Fertility and Sterility® Vol. 100, No. 6, December 2013 0015-0282/$36.00
Copyright ©2013 American Society for Reproductive Medicine, Published by Elsevier Inc.
http://dx.doi.org/10.1016/j.fertnstert.2013.07.2002
Yang, Z., Liu, J., Collins, G.S. et al. Selection of single blastocysts for fresh transfer via standard morphology assessment alone and with array CGH for good prognosis IVF patients: results from a randomized pilot study. Mol Cytogenet 5, 24 (2012). https://doi.org/10.1186/1755-8166-5-24
Anna M. Musters, M.D., Sjoerd Repping, Ph.D. et al. Pregnancy outcome after preimplantation genetic screening or natural conception in couples with unexplained recurrent miscarriage: a systematic review of the best available evidence. January 10, 2011. DOI: https://doi.org/10.1016/j.fertnstert.2010.12.022
Sin Yee Low, Colin Soon Soo Lee, Yun Xin Lim, Euploid blastocysts show a trend of higher implantation and
clinical pregnancy rates compared to untested blastocysts in
FET cycles https://www.rbmojournal.com/article/S1472-6483(16)30179-1/pdf