Science Pulse' 2012 Pacific Coast Reproductive Society (PCRS) Highlights
Genetic and Epigenetic Programs in Human Embryos
Each year, a team of physicians and staff from Pacific Fertility Center attend the Pacific Coast Reproductive Society (PCRS) annual meeting in Palm Springs, CA. One of the best talks of this conference was given by Dr. Renee Reijo Pera, Professor and Director of the Center for Human Embryonic Stem Cell Research at Stanford University.
She has also been able to map the process of human embryos expressing their genes. By the 4-8 cell stage of life, human embryos have to “turn on” their own genes and start making their own proteins. They first do this by destroying the maternal RNA (DNA messages) that originally came from the maternal genes in the egg. Then the embryo’s own DNA starts to make its own RNA messages. This finally ends with embryonic proteins being produced in embryos that are viable. Poorer quality embryos and those with chaotic, abnormal chromosome rearrangements are unable to do this properly and stop dividing.
It’s really only by scientists performing some of this essential work on early human embryos that we are going to be able to understand why some embryos make it and some don’t. And it is this understanding that is going to help us to select those embryos most likely to become a healthy human.
- Carolyn Givens, M.D.
Shedding light on the cause of miscarriage
Another interesting talk at this year’s PCRS meeting was entitled, “Recurrent Pregnancy Loss: Maternal and Fetal Causes.” The following is a summary of the information presented.
Miscarriages occur in 25% of all pregnancies, but even more frequently among women aged 35 and beyond. The majority of spontaneous miscarriages will occur in the first trimester, i.e. before 13 weeks gestation. As there are both paternal and maternal conditions which can cause miscarriages, a standard evaluation is recommended after two or more spontaneous losses. However, the results of this testing is going to be non-diagnostic in over 50% of cases because the majority of early pregnancy failures are secondary to fetal chromosomal abnormalities. Specialized genetic testing has also demonstrated these abnormalities to be mostly incorrect numbers of chromosomes (aneuploidy) and be due to problems in the individual egg nucleus during ovulation and /or fertilization. Thus couples confronting miscarriages will often experience significant frustration trying to learn the reason for their repetitive failures unless accurate evaluation of the fetal material is part of their overall diagnostic assessment.
Until recently the evaluation of fetal material after a miscarriage was frustratingly difficult. First, the tissue had to grow in culture in a special laboratory for a proper analysis (karyotype) to be possible. This meant collection of the material had to avoid bacterial contamination with special containers and media. The tissue had to be viable, i.e. able to grow, so it needed to be collected, packaged and delivered to the laboratory soon after it was retrieved. It was common to get a final report stating the tissue did not grow and no analysis was obtained. Second, when the fetal tissue was sent, there would often be indistinguishable maternal cells from the uterine lining attached. If tissue cells grew and an analysis was made, the diagnosis of 46 XX or normal female might represent the fetal or the maternal cells. There was not a simple method to distinguish between them.
Fortunately, the genetic testing company, Natera, now has a methodology for easily and accurately evaluating fetal material from miscarriages without the problems described above. Natera uses a SNP array with propriety technology called Parental SupportTM, which not only detects extra or missing chromosomes as accurately as a traditional karyotype, but also can distinguish maternal from fetal tissue. The fetal tissue does not need to be handled in any special fashion as cell growth is not needed for analysis. A specimen can be collected any time relative to the miscarriage and shipped from most anywhere to the Natera laboratory for analysis. The older technology of growing cells required 2-3 weeks for cell growth, while the new process can be completed and results provided within a few days. There is the need to include a specimen of maternal blood for comparative DNA analysis but this allows accurate discrimination between maternal and fetal material, eliminating the problem of maternal cell contamination. The Natera process can even accurately evaluate tissue from a pregnancy loss in the past which has been stored as a tissue block in a pathology laboratory. Additionally, the versatility of this test and its rapid results evidently do not compromise its accuracy as the reported failure rate was < 1%.
So we now have the ability to define those chromosome abnormalities which are so frequent in spontaneous miscarriages. As the cost is no greater than the previous less reliable techniques, it is cost effective as well. But most importantly, we can decrease the significant frustration for couples who have lost pregnancies but could never get a good explanation.
- Eldon Schriock, M.D.
PCRS is a voluntary, nonprofit organization deeply rooted in the continuing education of professionals in Reproductive Medicine. At this year’s PCRS meeting I had the pleasure of speaking in the same session as Dr Sherman Silber form St. Louis and Dr Nicole Noyes from New York University. Our topic was cryopreservation. I had been asked to speak on embryo vitrification in conjunction with genetic screening of embryos; while my fellow presenters both spoke on fertility preservation.
Dr. Silber has been a pioneer in ovarian tissue preservation for two decades. He presented impressive results; even though this approach, as it requires surgery, has not been a popular a method of fertility preservation. Silber has developed a technique of slicing the outer layers of the ovary into thin pieces (<1mm thick) and preserving the slices using vitrification. These slices can be warmed and transplanted at a later date. The technique of ovarian tissue preservation is not widely available, and the time to pregnancy can be long (some women in Silber’s series didn’t achieve pregnancy for over 3 years after transplantation). However, for most women ovarian function was restored in 2-3 months (reduction of FSH levels to normal values and production of estrogen). The ability to regain ovarian function is a big advantage of the technique, and the potential for long term ovarian activity is good (one woman had 2 children, the second of which came >6 years after the transplant). So the technique is probably best suited to young women with healthy ovaries who are not planning to have children in the short term future.
Dr. Noyes spoke about the more popular and more recently developed method of oocyte cryopreservation (egg freezing) as her preferred method of fertility preservation. Egg banks are becoming popular in the US based on the now established and reliable methods for vitrification of eggs. There are at least four banks that distribute vitrified donor oocytes nationwide, and this number is rising. As with ovarian tissue cryopreservation, oocyte vitrification is now a reliable and perhaps easier method for fertility preservation. The results with warmed oocytes are just as good as for oocytes that were never frozen. The number of live births from vitrified oocytes has shot up in the last 5-6 years because oocyte vitrification is now widely available, and so far there has been no increase in birth abnormalities when compared to the use of fresh oocytes. However, data for oocytes from women in their late 30’s and early 40’s is still scarce, since the technology is still young and many of these patients have not yet returned to use their oocytes. The little data available so far for these women suggests that pregnancy rates are similar to what would be achieved with fresh oocytes.
Dr. Noyes argued that oocyte cryopreservation is really the best option for fertility preservation since it maintains reproductive autonomy, gives the widest range of options for future fertility, and provides the highest chance for success.
- Joe Conaghan, PhD, HCLD