Pre-implantation Genetic Screening and Diagnosis (PGS / PGD)

Pre-implantation Genetic Screening (PGS) of embryos can be performed using biopsy techniques that evaluate all of the 23 pairs of human chromosomes contained within each embryonic cell. PGS technology is generally used so chromosomally normal embryos can be distinguished from nonviable and diseased ones and then prioritized for transfer. Because such chromosomal abnormalities are actually very common (demonstrated in over 80% of biopsied day 3 embryos from women over 40 years old, and even approximately 50% of day 3 embryos from healthy egg donors) PGS can be a powerful tool to identify those embryos that will never result in a successful pregnancy.

CT Fertility is offering several advanced PGS add-on options, including Mitochondrial PGS, a new technique which can probe beyond just the embryo's nuclear DNA, with the potential of further increasing success rates, lower the chances of miscarriage and reduce overall treatment costs:

  • PGS for embryo banking: The nuclear DNA of all embryos reaching the blastocyst stage by day 6 will be screened for chromosome abnormalities that may lead to reduced implantation rates and/or increase the likelihood of miscarriages. By batching the analysis of many embryos we can offer a reduced fee of $3,900. All embryos will be frozen for later use at the time of frozen embryo transfer.
  • Expedited PGS for fresh transfers: The nuclear DNA of all embryos reaching the expanded blastocyst stage by day 5 will be screened for chromosome abnormalities that may lead to reduced implantation rates and/or increase the likelihood of miscarriages. For a total fee of $4,900 the results will be expedited to allow for fresh transfer on day 6. All other blastocysts will be tested and frozen for possible future use.   
  • Enhanced Mitochondrial PGS for embryo banking: This $6,900 option evaluates both the nuclear and mitochondrial DNA of all embryos reaching the blastocyst stage by day 6, therefore offering a far more precise analysis of the potential of each embryo than traditional PGS. All embryos will be frozen for later use at a frozen embryo transfer.

CT Fertility is one of the few fertility clinics in the world that offers routine simultaneous nuclear and mitochondrial DNA testing as part of its PGS program. We believe that the technology is affording more of our clients an added level of reassurance, choice and control, and reaffirms our proven commitment to increase success without escalating costs.

Frequentjy Asked Questions - read here.

PGS and other PGD-based screenings are most frequently used in the following situations:

  • When the woman providing the egg is “older” and therefore at relatively high risk of treatment failure or pregnancy associated with miscarriage or birth defect. Such women have often already suffered previous miscarriages or numerous failed fertility treatments for reasons that may not yet be clear.
  • When a couple is at risk for having a baby with a specific genetic abnormality due to genes that either one (or both) of the genetic parents carry.
  • When single embryo transfer is planned to minimize the risk of multiple pregnancy.
  • When the parent(s) want to know the gender of each healthy embryo prior to transfer in order to pre-determine the sex of their child(ren).

Note that while many patients at CT Fertility choose to create their embryos and genetically test them before making any decisions regarding embryo transfer, some choose our “Test and Hold” option, which involves doing a fresh day 5 embryo transfer (which will result in a pregnancy most of the time) and then biopsying and freezing all the remaining normal appearing embryos for subsequent sibling projects. 

In recent years CT Fertility has already moved to offer advanced ‘Next Gen’ DNA sequencing to distinguish chromosomally normal embryos from nonviable and diseased ones. With the introduction of Mitochondrial PGS, CT Fertility is one of the first among a small group of pioneering fertility centers to take nuclear DNA PGS to the next step. Read below on how the technology continues to evolve to offer more successful and less costly surrogacy parenting options.


 

The continuing evolution of PGS technology

 

The key challenge of IVF has always been to create the healthiest embryos possible and to identify the ones that are most likely to develop well and result in a successful pregnancy. Given the health risk of multiple births for both the carrier and the future babies, the goal is to transfer the lowest possible number (often only one now) and still achieve the maximal impact (highest pregnancy rate).

Twenty years ago the best we could do was to grow embryos for three days before implanting them into the carrier’s womb, as few would survive longer in the laboratory. However at that early stage of development it was impossible to predict which embryos would further develop, and that meant transferring a higher number of embryos and “hoping for the best.” Unfortunately often the result was no pregnancy, and when was achieved, multiple pregnancies were common.

 

Patience is a virtue – also when it comes to embryo rearing

Over time science gained a better understanding of the nutrient sources for embryonic development and skilled embryologists were able to sustain embryos for 5-6 days so they could reach the critical “blastocyst” phase. At this stage it is much easier to determine which embryos will result in healthy live births, based on their rate of cellular growth and other gradable qualities.

Even with these far more effective blastocyst transfers, however, it was demonstrated that many of these highly graded embryos still had chromosomal abnormalities that led to reduced implantation or increased miscarriage. This heralded our next breakthrough – the ability to biopsy (before embryo transfer) each blastocyst to ensure that the genetics (chromosomes) contained in each cell's nuclear DNA were normal. This pre-implantation genetic screening (PGS) could thereby increase implantation rates and add a new level of safety, as well as reassurance that if the embryo were able to implant, subsequent miscarriage would be less common.

 

DNA sequencing of embryos without unpleasant tradeoffs

Early PGS techniques (particularly when done on 3-day old embryos) were associated with several drawbacks, including the risk of harming the embryo, and occasional false-positive results that led to discarding usable embryos. Luckily, further developments have allowed us to render those risks insignificant. This is especially true because most embryologists now only biopsy the outermost shell of the blastocyst without touching the fetal component.

 

Getting the complete picture with simultaneous nuclear and mitochondrial DNA testing

The most current state-of-the-art fertility treatments take nuclear DNA PGS to the next step by evaluating the "other kind of DNA" contained in the embryonic cell’s cytoplasm (not the nucleus) – the mitochondrial DNA, which directs the ability of the embryo to perform critical functions like cell division and implantation. Therefore even if an embryo has normal nuclear DNA it is far less likely to continue to grow after the transfer and successfully implant if mitochondrial DNA is not at appropriate levels. This latest generation PGS offers a far more precise analysis of the potential of each embryo than traditional PGS, with no tradeoffs.