August 16, 2010 Blog Post
Selecting the best embryo for transfer; what you need to know
One of the greatest challenges involved in infertility treatment is how to improve the pregnancy rate while also keeping the risk of multiple pregnancy (twins, triplets, etc) as low as possible. One strategy for achieving this goal is to let the embryos complete the development in the laboratory—the critical stage of becoming a “blastocyst”—that would normally take place in the fallopian tube. There are many so many studies that support this approach that it has been widely adopted by those centers that can confidently create the environment in the lab for healthy development to occur. Yet this technique still has limitations. One study [G1] recently demonstrated that nearly half of the best looking blastocysts are still genetically abnormal, even for women less than 40 years of age. Embryos selected for transfer before they reach the blastocyst stage only have about a 40% chance of being genetically normal. These studies have driven an interest in making preimplantation genetic screening (PGS) available to more couples going through fertility treatment. To do so can maximize embryo selection as well as provide useful diagnostic information to couples undergoing IVF.
The goal of any fertility program should be one embryo per transfer. But since it is so difficult to predict which embryo is most likely to implant and become a healthy baby, a common strategy is to transfer more in the hope of boosting success. This is often done with the knowledge that if a chromosomally abnormal embryo implants, it has a 99% of miscarrying; compared to a 7% risk of miscarriage for a normal embryo. So PGS can not only boost the pregnancy rate per embryo transferred, it can also reduce the risk of miscarriage as well. Previous studies [G2] questioning the benefits of PGS have been thoroughly analyzed and found that the techniques and the technicians had a big impact upon limiting the successful application of this new tool in those headline-grabbing stories. Emerging research suggests that using PGS to select embryos may result in a pregnancy per transfer rates of 80% or higher; even in high risk patients. The key is to only transfer the embryos that are genetically competent.
Now that the techniques for embryo biopsy and genetic testing have been refined and made more accessible, the challenge is selecting which couples are most likely to benefit from this technology. The goal is to minimize the cost of treatment while also optimizing the outcome. A recently published but exhaustive review [G3] this subject summarized the key selection criteria needed to achieve that goal. Here’s what you should consider as you decide whether or not you’re interested in PGS:
- Couples where the egg comes from a woman that is at least 37 years of age; the time when genetic abnormalities naturally increase in frequency
- There are at least 5 healthy embryos (Grade 1 or 2 with at least 6 cells present) available for testing
- There are at least 8 chromosomes tested including 13,15,16,18, 21, 22, X and Y (the ones most likely to be abnormal)
- Embryo biopsies are only performed by properly trained personnel (>100 biopsies within the last few years with an average of 5 minutes or less per biopsy) to avoid unnecessary damage to the embryo
- Established techniques are used for biopsy preparation
- All samples are sent to experienced labs with strict quality assurance standards
- IVF center has extensive experience in counseling patients and explaining results
2 thoughts on “”
In general, for 3DT is a higher cell count favorably associated with pregnancy. Is a 10 cell embryo on day 3 more likely to implant than an 8 cell provided they both look good and have little to no fragmentation? I have 3 frozen embryos for FET – 6 cell, 8 cell and 10 cell. I would like to avoid multiples and plan to do an eSET. Would you choose the 10 cell?
It is very easy to over-interpret the issues related to cell number on Day 3. What I have typically offered patients in the sort of predicament that you describe would be to thaw and incubate all three frozen embryos. By Day 5 (or 6) you should be able to clearly see which makes the healthiest looking blastocyst. Since this blastocyst stage is the one that normally represents embryos ready for implantation, this will give you your best selection. If all three make excellent looking blastocysts, you can transfer one or two and simply refreeze the third one. Most labs should be able to accommodate this request. I do hope this suggestion helps.
~Robert Greene, MD, FACOG