By the end of the year we will have started a new and very exciting research project in our lab. We have partnered with a company called Incept Biosystems (www.inceptbio.com) to do a clinical trial of a new embryo culture system called microfluidics.

The traditional culture dish with medium droplets under oil as described by Brinster, R.L., 1963, Exp. Cell Res., Vol. 32

This involves culturing embryos in very small volumes of culture media inside a chip specifically designed for this purpose. Tiny pumps regulate the flow of culture medium in and out of the chip without causing the embryos to move around.

The traditional vessel for embryo culture is the petri dish, where small droplets of culture medium are overlain with a highly purified mineral oil. The culture medium, regulated in much the same way as pharmaceuticals, is one of the most highly tested and expensive components of the IVF laboratory operation. We typically make droplets of medium that are in the 50-200µl size range, and the oocytes or embryos are placed in the droplets for 24-48 hours at a time. This is a static culture system where nutrients are depleted by the developing embryos and waste products (e.g. ammonia from amino acid breakdown) accumulate over time. The droplets are large enough to make sure that the supply of nutrients is more than adequate and that waste is diluted to the point of not harming the embryo in any way. The embryos are changed into fresh medium at least every 48 hours.

This system for embryo culture has been in use since human IVF began in the late 1970′s and early 1980′s. It was actually developed in the early 1960′s by a pioneer of mouse embryo culture, Dr Ralph Brinster, at the University of Pennsylvania. Some early human embryologists cultured embryos in small test tubes without the mineral oil, but nowadays, despite the age of this technique, it is very unusual to find a facility that does not use the droplets under oil method. After 45 years, perhaps it is time for a change?

A microfluidic system for embryo culture has been in development for over 5 years at the University of Michigan in Ann Arbor. Professor Gary Smith combined the talents of his graduate students in physiology with those of engineering students and came up with a device that has had outstanding results with growing mouse embryos. Professor Smith is no stranger to IVF, as he was the director of the University’s IVF Laboratory for many years and he was instrumental in designing and testing the vitrification system that we now use to preserve oocytes and embryos. He solicited venture capital to start Incept Biosystems with the intent to bring microfluidics into human IVF labs. Incept Biosystems were onsite at PFC during the last week of October to train our embryologists on the use of the system. We did several trials with mouse embryos to achieve proficiency with the system and then we will actively recruit patients to enroll in a clinical trial using the system.

The clinical trials are being run at 3 centers in the US. In addition to PFC, patients will participate at the Fertility Center of San Antonio and at Southeastern Fertility Center in Charleston, South Carolina.

A schematic of a microfluidic embryo culture device with fresh medium in blue and spent medium in red. The embryo is contained at the base of the chamber, where the blue medium ends.

Patients that are asked to participate will have to consent to the study, where their embryos will be divided into 2 groups for culture in the microfluidic device and in the traditional petri dish. The culture media will be the same for all the embryos, but half will be in a replenishing media current (microfluidics) and half will be in our traditional static culture.

Microfluidics has had impressive results with mouse embryos where it significantly increased rates of development and implantation over those for embryos grown in static culture. Cell numbers for the microfluidic embryos were almost twice as high as for traditional culture (110 vs. 65), and pregnancy rates from transferred embryos were increased by 22%. Incept Biosystems have tested the new technology extensively and have been able to obtain surplus IVF embryos donated for research for human trials. There are some nice videos on their website that showcase the equipment and procedure, and detail the mouse embryo results. Professor Smith presented the results and won the prize paper at the 2008 American Society for Reproductive Medicine (ASRM) meeting (Smith et al., 2008, Fertility and Sterility, Vol 90, pages S1-S2), and these results will soon be published in a peer reviewed journal.

We will be asking for participants to join the study, beginning in November and continuing for 2-3 months. This is a short study requiring enrollment of only 20 patients, but a larger study is planned for next year subject to favorable outcomes here. If you are interested in the study and would like more information, please ask your physician at your next visit.

For patients having their embryos transferred at the blastocyst stage, the grading procedure used to assess the embryos can seem complicated. However, we simply look to see that the embryos are developing normally, are not slowing down, and are preparing for implantation in the uterus.

In the 2 days following fertilization, embryos go through 3 rounds of cell division. The fertilized oocyte divides in 2, these cells each divide again to give 4, and then these divide to give 8. In the resulting 8-cell embryo, each cell should be 1/8 the size of the original oocyte since there is no growth in size, and each cell should be intact and symmetrical. When we assess embryos at this stage, we first count the number of cells and we then assign a grade based on how good the embryo looks. Embryos that have disintegrating or asymmetrical cells are assigned a lower grade.

At this early stage, the individual cells stay together because they are contained within a shell called the zona pellucida. However, as the embryo progresses past the 8-cell stage, dividing to 16 and then 32, the cells attach to each other and cooperate to form a tight ball called a morula. At the morula stage, the cells are pressed so tightly together that individual cells cannot easily be identified or counted. Once the attachments between cells are formed, the cells begin to pump fluid into the center of the ball, giving rise to a tiny fluid filled cavity or cyst. As long as the junctions between cells hold, no fluid can escape from the cyst, and the cyst grows larger as more fluid is pumped in.

These are critical days for the embryo. In addition to forming the central cyst, the embryo is also busy organizing its cells into two distinct populations. As the embryo moves beyond the 8-cell stage, some cells stay on the outside of the ball and some are pushed to the inside. In the typical 16-cell embryo, there are 12 outer and 4 inner cells. At the 32-cell stage, 22 of the cells are outer cells and 10 are inner cells. Creating more outer cells is deliberate, because these cells are needed to maintain the integrity of the cavity as it becomes larger. More importantly however, these cells will become the placenta, and having enough cells to establish the placenta is critical to successful implantation in the uterus. Once the placenta is established, it can feed the inner cells which become the developing fetus.

The appearance of the cyst at the center of the morula marks the next embryo stage, the blastocyst. In assessing the blastocyst, we look at the size of the cyst and the integrity of the outer and inner cells. Depending on the size of the cyst, the blastocyst is referred to as early, expanding or fully expanded. If the cyst has become large enough to cause the embryo to burst through its shell, we call it a hatching blastocyst. Occasionally, we even see fully hatched blastocysts. Hatching is a natural process that frees the embryo from its shell to allow implantation to occur. The more expanded the cyst has become, the more we favor the embryo for transfer.

In addition to looking at cyst expansion, the grade of the blastocyst is further determined by the integrity of the inner and outer cells. Embryos with more cells are better, and the best blastocysts are well expanded with distinct inner and outer cell populations. In poor quality blastocysts, there can be few cells in one or both populations, and/or the cavity can be small. And sometimes, even in embryos with beautiful outer cells, we cannot see any inner cells at all. These embryos are destined to fail since a full blastocyst with 32 cells is incapable of making inner cells if they do not already exist.

The embryos that are most difficult to assess are those where the cavity has just begun to open up, but has not expanded sufficiently to allow us to see inside. These early blastocysts are usually assigned lesser grades as we are unable to determine whether any inner cells are present. We often look at these embryos again several hours later to see if further expansion has revealed the presence of those critical inner cells. We would then re-grade the embryo, if appropriate.

All of this development, from fertilization to blastocyst expansion and hatching, normally follows a tight timeline that is independent of cell number. The embryo attempts to hatch from its shell approximately 5 or 6 days post fertilization, regardless of the number of cells it contains. If development is slow, and cell number is consequently low, the outer cells stretch to enclose the cyst and expansion continues. This is important, as the uterus waits only a few days for the embryo to implant. If the embryo takes too long to make the “right” number of cells for expansion and hatching, it may miss the implantation window. The practical result of this is that we still get high implantation rates even if only early blastocysts are available for transfer.

The above phenomenon is relevant to frozen embryo transfer cycles too, because many embryos lose one or more cells as a result of freezing and thawing. Such embryos still try to form blastocysts according to their original timeline, even though they may have less than the ideal number of cells. The consequences of arriving with plenty of cells but too late for the uterus are worse than having a chance to implant even with fewer cells. As a result, frozen-thawed embryos that have lost a cell or two are not assigned a lower grade since we still consider them to have high implantation potential.  

Question: I am an educator for a human sexuality class. A student asked me an interesting question that I was unsure how to answer. Given that we know sperm can survive about 72 hours in a woman’s body, how is it possible to keep sperm viable by freezing them?

Answer: Sperm can survive for a long time under the right circumstances. In a woman’s body we think that 72 hours is approximately correct, but the data supporting this estimate is not conclusive. In the lab, sperm can live 5 days or more provided they are removed from the seminal fluid and placed in a more nurturing environment. Seminal fluid contains many enzymes that first clot and then liquefy. This change in the fluid allows the ejaculated sperm to stay in the vagina initially, but then swim out as the seminal fluid becomes more liquid. These enzymes quickly destroy any sperm that can’t swim out of the semen within a few hours.

It takes approximately 72 days for sperm to mature in the body. During the last 14 days of this process, the sperm are very much alive and swimming. They are alive a long time prior to leaving a man’s body.

During freezing, sperm are cooled to a very low sub zero temperature (minus 196 degrees Centigrade). At that temperature, all biological activity is effectively stopped. The sperm cells are not metabolizing or depleting their energy reserves. They are truly in suspended animation. Bacteria or other microbes cannot attack or degrade the sperm in any way because they are also unable to function at such a low temperature. Everything is on hold.

Biologists believe that correctly frozen cells in long term storage can literally last forever, as long as the temperature is properly maintained. It is believed that constant exposure to normal levels of background radiation is the only thing that could cause loss of viability and this effect is difficult to measure. Studies done in the 1970’s, exposing frozen mouse embryos to the equivalent of 2,000 years of background radiation, showed no measurable mutagenic effects in offspring.

Cryobiology is a relatively new science, and human fertility treatments are newer still. Consequently, in humans there are no long term results with frozen sperm or embryos. There are a handful of reports showing babies born from embryos that had been frozen for 12-15 years. A couple in New York had a child in 2005 from sperm that had been stored for 28 years. Sperm frozen for domestic animal species have a longer record because samples frozen in the 1950’s are still viable.

The process used for freezing is very precise and works best when cells exist individually (such as sperm) or in very small groups (such as an embryo). Larger masses of cells, tissues or even whole bodies cannot be frozen and subsequently thawed alive. It is not currently possible to freeze and thaw a whole ovary or kidney.

To successfully freeze cells we must remove cell water (water expansion during freezing would burst the cell) and replace the water inside the cell with antifreeze. This is done by incubating the cells in a solution of antifreeze. The water and antifreeze swap places through the process of simple osmosis. In a complex tissue like an ovary, there is no way to get all the water out of all of the cells so easily, thus a whole ovary cannot be frozen. If the ovary is chopped up into tiny pieces however, more water can be extracted. Some success has been reported with freezing ovarian pieces in this way.

The following student experiment demonstrates the challenges of freezing. Place a whole peach into your freezer for 24 hours and then thaw it out and see what a mess you have. If however you slice the peach up and mix the slices with sugar for 15 minutes (the sugar will draw out water from the cells), you can freeze the peach quite successfully. If the technology is used correctly, you can keep your peach (or your sperm) for leaner times.

Joe Conaghan, PhD, HCLD

Every year, several Pacific Fertility Center professionals participate in ASRM’s national meeting. They evaluate the research and share their findings with PFC and Fertility Flash.

Among those attending the conference from PFC were Dr. Philip Chenette and Dr. Isabelle Ryan and Peggy Orlin, MFT. Their reviews cover the following topics: Update #1: Ovarian Stimulation Techniques, Update #2: PGD and Aneuploidy Screening Techniques, Update #3: Egg Freezing, Update #4: Acupuncture, and Update #5: Men and ART.

ASRM Update #3: Egg Freezing

Oocyte cryopreservation is the storage of the female gamete, the egg, prior to fertilization. Preservation of fertility for single women that must undergo cancer therapy or surgery, or that must delay or choose to delay childbearing, and donated oocyte banking are all applications of oocyte cryopreservation. The need for this technology is clear, but reports of success with oocyte cryopreservation have been limited.

Highly successful oocyte cryopreservation is now attainable. New studies are showing pregnancy rates with oocyte cryopreservation that are equal to traditional IVF techniques.

The key to this technology is oocyte vitrification – an ultrarapid cryopreservation technique. Researchers from Atlanta described their experience with vitrification. Out of 11 patients with transfers, nine conceived, with an implantation rate of 65%.

Pregnancies after oocyte cryopreservation have developed normally. An Italian study of 105 children born after oocyte cryopreservation showed no problems. A Chicago study of the genetics of oocytes, embryos, and children born after oocyte cryopreservation was reassuring. No increase rates of aneuploidy or malformations were reported, and normal development was found in post-natal follow-up.

These results are similar to those we have previously reported from our own research at Pacific Fertility Center (see December 2007 Fertility Flash). Oocytes are now cryopreserved with high success rates. Oocyte cryopreservation technology has matured, and we look forward to providing these techniques for our patients.

Philip Chenette, MD

In late October of this year, our first patient who underwent embryo transfer with embryos created from vitrified and warmed donor oocytes has successfully delivered. The baby was born at term and appears to be perfectly healthy.

Three other pregnancies are ongoing and are expected to deliver in 2008. We congratulate our new parents and the parents-to-be who have participated in this ground breaking program.

PFC has ended enrollment of patients into this program, but expects to continue research efforts with respect to oocyte vitrification.

While it has been possible to preserve sperm for many years (the famed Dutch microscopist Anton von Leeuwenhoek allegedly cooled and then recovered sperm using snow and ice in the 17th century), reliable methods for oocyte preservation have been elusive.

We previously discussed some of the problems with oocyte freezing (see Fertility Flash, January 2005, Volume 3, Issue 1), and now report our success in overcoming some of the obstacles.

Traditionally, preservation of sperm and embryos has been achieved with the use of a technique called slow freezing. This process incubates the sperm or embryos in low concentrations of cryoprotectants (antifreeze) to draw water out of the cells. After this incubation, they are cooled very slowly to sub zero temperatures. Typically this slow freezing technology just works for cells that exist individually (such as sperm), or together in small numbers (embryos), as the water must be extracted from every cell. Tissues, which are made up of many hundreds of thousands of cells, cannot be dehydrated successfully and therefore cannot be frozen intact. Cells in the tissue can burst when the water remaining in the cells expands as it turns to ice. For example, it is not possible to freeze a whole ovary, but some success has been achieved with ovaries that were cut into tiny pieces.

Frustrated by the lack of progress with slow freezing, scientists have more recently moved towards a technology called vitrification for oocyte preservation. Vitrification, which was described in detail in September’s Fertility Flash (Volume 5, Issue 8 ) works by using higher concentrations of cryoprotectants and much faster cooling rates. Cells are typically cooled in tiny straws (see article heading). This process allows us to achieve cooling rates of several thousand degrees per minute.

When vitrification straws and cryoprotectants were first approved by the FDA for human embryos, PFC began the process of adapting the technology to oocytes. Our embryologists attended training courses and became proficient with the technology by practicing on mouse and hamster oocytes and embryos. Even though we have been handling oocytes and embryos for many years, this technology provided many new challenges, mainly due to the tiny size of the straws and the speed at which the cells had to be cooled. Once we became proficient with the procedure, we began to freeze high quality oocytes from donors who had proven fertility. In this way, we knew that if the procedure did not work, it would be the vitrification technology and not the oocytes that were to blame. In addition, we satisfied ourselves that the technology was safe by looking at the exhaustive work by Dr. Gary Smith at the University of Michigan, which showed that vitrified/warmed oocytes were both physically and genetically normal and that the resulting pregnancies and babies were healthy.

We recruited five oocyte donors and vitrified all of their oocytes immediately after their oocyte retrieval procedures. We then offered the oocytes to individuals who were on our waiting list to accept donated embryos. Typically, these individuals were unable to get pregnant with their own oocytes or financially unable to proceed to an egg donor cycle. The availability of the vitrified oocytes was a great alternative to accepting donated embryos as it allowed couples to choose their own sperm source. Furthermore, the immediate availability of vitrified oocytes was an attractive alternative to what may be a very long wait for donated embryos.

Pacific Fertility Center had immediate success with the first recipient. We had vitrified 16 oocytes from the first donor, and for the first recipient we warmed only 7 of these. Four hours later we injected a single sperm into each of the 6 oocytes that appeared alive and healthy (1 oocyte had not come through the process successfully). The next morning, 3 of the oocytes fertilized normally. After 2 more days, we had 3 nice embryos for transfer. The positive pregnancy test 11 days later, and a singleton pregnancy confirmed by ultrasound at 7 weeks were great rewards for our efforts and thrilling news for the recipient. Our second recipient used a different donor and although her pregnancy started out well, she miscarried in the first trimester. Our disappointment over this loss was compounded when we discovered the oocytes from 2 of the donors did not survive well when warmed. In these particular donors, we recovered high numbers of oocytes (each had close to 40) and for unknown reasons their oocytes were overly sensitive to vitrification. The next three donor cycles proceeded well and resulted in pregnancies. These 3 pregnancies are all ongoing at the time of writing. We will update readers with their outcomes at a future date.

Although we were warming relatively small numbers of oocytes (typically 6 or 7), we began to have more embryos than could be safely transferred to recipients. Our first pregnancy had been achieved after transferring 3 embryos. It is more typical, however, to transfer only 1 or 2 embryos when donor oocytes are used. Even when using only 2 embryos, multiple pregnancy rates were unacceptably high. Understandably, few patients are willing to risk a decreased chance of conceiving by transferring only a single embryo. In order to avoid high multiple pregnancy rates in a typical IVF cycle, embryos are usually cultured for 5 days to determine which embryos in a cohort have the best chance of establishing a pregnancy. However, if a patient has only a few embryos, the benefits of extended culture are less, and the transfer is typically done after only 3 days growth. With our recipients of the vitrified oocytes, we began by doing 3-day transfers. Once high success rates were evident, we elected to implement day-5 transfers, in an effort to decrease high order multiples. The last 2 pregnancies both resulted from day-5 transfers of 2 embryos each, and they are both twin gestations.

In summary, we have had 7 out of 10 embryos implant after transfer (excluding the 2 failed donors with the high oocyte numbers). This implantation rate (70%) is comparable to the implantation rates that our patients have when using fresh embryos from donor oocytes.

We are moving forward cautiously with our oocyte vitrification program and hope to use the remaining oocytes soon. While these results are encouraging and have brought great joy to a small number of our patients, there are more issues to resolve before we declare complete success. The 70% success rate was obtained with the use of the highest quality oocytes from young donors who were known to be fertile and healthy. We have already seen that some oocytes are less tolerant of the procedure, as evidenced by the results from the 2 donors with high oocyte numbers. We also fully anticipate that the results for older women using their own oocytes will be worse, as they are for these same patients using a fresh IVF cycle. In fact, at this time, we do not have any idea if the oocytes from women in their 30’s will be able to tolerate vitrification.

Going forward, we will offer oocyte vitrification unconditionally to women with cancer who are likely to be left sterile by their treatment. For these women, and for others who elect to vitrify oocytes for social reasons, we will exercise great caution in our estimates of future pregnancy potential with the warmed oocytes. Until we have more data with oocytes from a variety of women, we will have no way of telling if there is any hope from anything other than donor oocytes. That data will accumulate more slowly because women who elect to preserve oocytes are not likely to be using them for some time. For now, until there is more data, we continue to believe that embryo freezing has the greatest potential for those wishing to preserve future fertility. However, for those who are single and in their late 30’s, we will be reluctant to recommend oocyte vitrification as a reliable fertility preservation method. Hopefully, they will find Mr. Right before we have objective data.

Joe Conaghan, PhD, HCLD

Question: We hope to have embryos left after transfer and need to consider storage. Can you help us understand what determines your storage fees?

Answer: Many Pacific Fertility Center patients have surplus embryos at the end of their IVF cycle. If you chose to freeze your embryos, you will need to consider how long you plan to store the embryos before being used for a frozen embryo transfer. Patients who are finished building their family, but are not interested in destroying the surplus embryos, may choose to freeze them, offer them for adoption or donate them to research. These options are included on the consent forms, which must be signed prior to transfer.

Once you choose to freeze embryos, you need to factor in the annual storage fee. Pacific Fertility Center strives for lower fees, but must be able cover the underlying costs of services. Storage fees include expenses from the following sources: storage tanks, liquid nitrogen, leased floor space, embryologists and staff hours, equipment maintenance, annual inventory, information dissemination, forms, billing, legal fees and liability.

Let’s begin with the storage tanks themselves. At PFC we have 3 state-of-the-art embryo tanks: two tanks hold a total of 1376 spaces each. Every one of these spaces can hold up to 5 straws of embryos and each straw holds 1 to 3 embryos. These two tanks are full. Recently, we purchased another, larger tank, which holds almost 1500 patient spaces. This tank is already almost half full.

Once these tanks are filled with liquid nitrogen, they are extremely heavy. Because of their weight, they cannot be clustered together in the same room, but must be strategically placed to spread out the weight over the center’s floor. In addition, they must be stored in a secure, locked location. Every time we add a tank, an appropriate new space must be located. With square footage at a premium, this is not an easy task.

Storage tanks must be monitored. Gauges and seals must be functioning and the temperature must be kept at the optimum level with the addition of liquid nitrogen. The tanks are fitted with an alarm, which sounds if there is a problem. This alarm automatically sends an alert to the embryologist on call 24 hour a day, 365 days a year.

All embryo straws are labeled and a file is maintained for every patient who has embryos in storage. This extremely important aspect of storage is taken very seriously. A thorough inventory is completed every year. This is a time-consuming process as every straw must be located and identified. Patient addresses are kept up-to-date and confirmed annually when the invoice is sent or when patients notify the center of an address change.

If patients fail to notify us of a move and/or abandon their embryos, we make every effort to locate them. When they repeatedly fail to pay their invoice, we may be forced to send their billing on to a collections agency. During this process, we continue to store their embryos. As a last resort, we will go before a judge, show proof that we are unable to contact the patient after multiple attempts over a reasonable period of time, and request permission to discard the abandoned embryos.

One of the most frequently asked questions is “When am I going to be billed?” You will be billed based on the month that your storage begins. Patients often forget they have a back-up sample of frozen sperm and are “surprised” when they receive an invoice indicating they must pay their storage fee.

PFC is always available to answer any questions you may have regarding the storing of your embryos and sperm. For disposition questions, please contact Alexis Von Austin, Tissue Bank Manager at (415) 249-3636. For questions regarding an invoice, please contact Rosemarie S. Tagle, Billing Supervisor at (415) 249-3651.

Fresh Embryo at Blastocyst Stage: The cells are elongated and pressed against one another. The inner and outer cells are clearly visible, as is the cavity.

Two Vitrified Embryos at Blastocyst Stage After Warming: Though their appearances differ, both embryos implanted and created viable pregnancies.

This embryo looks perfect, as if it was never frozen. The outer and inner cells are clearly visible, as is the cavity.

This embryo has rounded, more dissociated cells resulting from shrinkage during incubation in cryoprotectant, (as cells shrink they pull away from each other). The cavity is small, but visible.

The first human pregnancy from an embryo that had been frozen and thawed was achieved in Australia in 1984, 6 years after the birth of the first IVF baby in the UK. The method used to preserve that embryo is called “slow freezing” and it is still the preferred method for preserving embryos throughout the world today. Slow freezing is a reliable and established technique that has served the IVF community well for over 20 years. The procedure has been refined throughout those years and it works, with slight modifications, for freezing all embryo stages and for sperm. However, despite many years of trying, slow freezing has never worked very successfully with oocytes. Frustrated by years of failures, scientists turned to an alternative procedure called vitrification in their quest to preserve oocytes. This approach is relatively new, but appears as through it will be preferentially used for oocyte preservation as we go forward. Vitrification kits are just beginning to get FDA clearance following scientific trials, and embryologists are being trained in the use of the new technology.

The main concern during the freezing of any cell is the removal of water without actually killing the cell. Since water expands in volume as it freezes, ice formation inside a cell would cause the cell to rupture and die. Therefore, cell water is traditionally replaced with a cryoprotectant (antifreeze) prior to cooling of the cell. This is achieved by sequentially incubating the cell in increasing concentrations of cryoprotectant. The cryoprotectant draws water out of the cell and itself enters the cell, all by osmosis. Once most of the water has been removed, the cell is cooled at the very slow rate of -0.3° C/minute until it has been cooled to below -30° C and is therefore fully frozen. Thereafter, storage of frozen cells is in liquid nitrogen (-196° C), which is a simple and practical storage medium.

Vitrification still requires the use of cryoprotectants and the cell is also ultimately stored in liquid nitrogen, but the journey from the incubator (at 37° C) to the nitrogen (-196° C) is much faster. The word “vitrum” in Medieval Latin means “glass” and the process turns the cell contents to a glass like substance instead of ice. Since no ice forms, the risk of rupturing the cell is eliminated. For glass to form instead of ice, the rate of cooling must be thousands of degrees per minute instead of the 0.3 degrees/minute that we use in slow freezing. Therefore, the process is sometimes referred to as ultra-rapid freezing, although the word “freezing” is really inappropriate here since the cell is not really frozen (i.e. no ice is created).

One of the big stumbling blocks during oocyte freezing was the sheer size of the cell (the oocyte is the largest human cell by some margin) and therefore its high water content. Just getting the cell to survive, (an oocyte has only one cell), was a huge stumbling block. Studies where 50-60% of the oocytes survived were considered groundbreaking, and still today there are few studies that have done better. Vitrification as a technique had been largely ignored by the IVF community as it was technically more challenging and used much higher concentrations of cryoprotectants. Cryoprotectants were thought to be toxic to cells. Today we know that they are safe and effective and do not contribute to cell death. It is possible that cryoprotectants may have deleterious effects on cells if they are metabolized, but virtually all freezing protocols utilize them at room temperature or below, where cell metabolism is significantly slowed or stopped. So, with success rates using traditional slow freezing failing to improve, vitrification has been given serious consideration as an alternative. In the few years since its introduction, vitrification has shown promising and excellent results in clinical studies (see Oktay et al., Fertility and Sterility, 2006, Vol 86(1), pages 70-80 a comparative review of slow freezing and vitrification results with human oocytes).

Making the transition from slow freezing to vitrification has been a challenge for the IVF community. As already stated, it is a technically challenging procedure, and training of embryologists in the technique has been slow. With slow freezing, embryos are placed in relatively weak solutions of cryoprotectant for as long as 15 minutes at a time. Then, they are usually moved on through slightly stronger solutions before being placed in large straws or vials which are then loaded into a computer controlled freezer for the long journey to -30° C. The embryologist can spend about 30 minutes with a set of embryos from the time that they come out of the incubator until they go into the controlled rate freezer. After 2 or more hours, the embryos can be placed in liquid nitrogen and the process is complete.

During a vitrification procedure, where typically only one oocyte or embryo can be worked on at a time, the transition from incubator to nitrogen takes only a few minutes. The embryo is stepped through solutions containing high and then higher concentrations of cryoprotectants where it shrivels and swirls in the extremely viscous medium. In the final stage, which is measured in seconds, the embryo is placed in an extremely concentrated cryoprotectant solution and then quickly loaded up into a tiny straw that is barely larger than the embryo itself. The straw is then sealed at both ends and plunged immediately into liquid nitrogen. The straw is so fine that it freezes in an instant, an important part of the vitrification process. The loading of the straw occurs at room temperature (25º C in the IVF lab) and it is cooled to -196º C in one or two seconds, giving a cooling rate of 6000-13000º C/min. The faster the straw can be cooled, the more successful the procedure. Performing this final step too slowly or too quickly can be the difference between success and failure and therefore requires extensive training.

At Pacific Fertility Center, we have been working on vitrification for over 2 years. Our initial interest was in oocyte freezing, but we were also interested in extending the technique to be used with embryos, and in particular to blastocyst stage embryos where slow freezing has not always worked well. Slow freezing has served us well over the years for embryos being frozen 1, 2 or 3 days after an oocyte retrieval, but blastocysts (5 or 6 day old embryos) did less well. With an industry wide transition to blastocyst stage embryo transfers, we looked at vitrification as an alternative method of preservation for these precious embryos.

A blastocyst is an embryo that has developed to the stage where it is ready to implant in the uterus. Instead of having a small number of loosely associated cells characteristic of earlier embryonic stages, it has 2 defined cell populations and a fluid filled cavity (or cyst). The cells that surround the cavity will form the placenta, and the cells within the cavity will develop into the embryo proper, or fetus and some of the extraembryonic membranes, such as the yolk sac. It is these interior cells that cause trouble during freezing since they are on the inside and difficult to expose to cryoprotectant. Slow freezing relies on cryoprotectant traveling through the outer placental cells, then the cavity, and finally into the fetal cells while water travels in the opposite direction. Fully dehydrating these fetal cells has always been a challenge and an embryo where these cells do not survive freezing and thawing will not result in a viable pregnancy. And with slow freezing, embryos tend to collapse in on themselves during dehydration, making it difficult to assess survival after thawing.

After investing heavily in vitrification training and implementing a successful oocyte vitrification program, PFC began working on blastocyst vitrification in January of 2007. By March we had a program established and were delighted by how easily blastocysts seemed to tolerate the procedure. Often, blastocysts looked no different after vitrification when compared to how they looked before the procedure. This result was in stark contrast to slow freezing where blastocysts always look shriveled and deflated after coming out of the freezer. By July 2007, we had switched completely to vitrification and currently we are enjoying the successes that it is bringing to our patients and us.

Our vitrification team consists of 3 embryologists: Mariluz Branch, the team leader, with Erin Fischer and Liz Holmes. Because of the technical challenges involved, we have to be cautious with involving other embryologists. So one of the three team members must be on duty every day (our lab is open 7 days a week). I am grateful to this team for their flexibility in accommodating our needs. By the end of the year we expect to have 2 more embryologists on the team, and then the final 3 in 2008.

Vitrification has been an exciting and challenging technique which we have embraced and conquered in 2007. We look forward to the gradual elimination of slow freezing and the successes that vitrification will bring us in the future.

Joe Conaghan, PhD, HCLD

Tuesday February 1st was a busy day here at Pacific Fertility Center. The front office was busy with their usual patient appointments, comings and goings for consultations, ultrasound scans and blood draws. In the procedure area and the lab, we were having one of our busier days, with 7 retrievals, 5 fresh embryo transfers and 1 frozen embryo transfer scheduled. It’s rare for us to have so many procedures on a single day, but because the exact date of a patient’s retrieval is uncertain and depends on their response to stimulation drugs, we get a day like this a few times per year. Fortunately, PFC has an exceptionally large and well-equipped laboratory, so we can cope easily with variations in case load. Also, both our nursing and embryology staff schedules are flexible enough to allow us to schedule extra staff when necessary. On that Tuesday for example, we had 8 of our 9 embryologists on duty in the lab

Even though most patient appointments don’t happen before 8 AM, lab and nursing staff are here between 7 and 7:30 in the morning to open up the facility and perform the usual quality control (QC) checks before the work day can begin. In the lab, once all QC and start-up procedures have been completed and documented, we begin looking at embryos that are to be transferred that morning, thawing frozen embryos for transfer, evaluating fertilization for the previous day’s patients, retrieving eggs and processing sperm samples. The nursing staff is busy checking in patients for retrievals, doing all their pre-operation checks and setting up IV bags, and coordinating patients for embryo transfers. Mornings are definitely our busiest time; we do this every day (7 days a week) so we like to think that the work flows smoothly.

At approximately 8:30 AM, right in the middle of the action, the power to our building and to those in a 10-block radius, went out. When a power outage occurs, there’s a split second when everything goes dark, but before you can think about it, emergency power kicks in and we almost seamlessly continue working. However, as part of our procedures for disaster preparedness, we have protocols for working during a power outage, and these immediately become active. First we check our emergency power generator and then all vital equipment to make sure that everything has power and is functioning normally. In the lab, one of our 15 incubators reset itself and went into calibration mode, so we simply moved its contents to a new home. No other problems or incidents occurred that day. We completed all retrievals and transfers in the usual way and our biggest concern was simply wondering why the power had gone out.

On the nursing end, patients were escorted up and down 5 flights of stairs because the elevators shut down, but otherwise their day was uneventful.

Emergency procedures and back-up power are a vital part of our operation. Our emergency generator will run our facility for 36 hours, or longer with the addition of diesel to the tank. The generator gets a 30-minute test run and an inspection every week. It receives a full service a minimum of 4 times a year and immediately after any power outage. After this instance, a service technician checked the generator and refilled the tank.

In the event there is a power failure when no one is present, the system will automatically switch over to back-up power. The alarm system in the lab then proceeds to dial each embryologist in turn on his or her home and cell phones until the call is received and verified with a code. All vital equipment is alarmed which enables us to check the status of the equipment from a remote location. We also have auditory monitoring capability and can listen to the background noise in the lab (such as a fire alarm) at any time. If it is necessary, we are prepared to have an individual physically present in the lab within 30 minutes of getting an alarm call.

Embryos and sperm in freezers don’t actually need power at all, provided that we physically fill the cryo tanks with liquid nitrogen once or twice a week. The computers that usually monitor and automatically fill these tanks do need power of course, but they are not essential to maintain refrigeration.

On February 1st, power was restored after 90 minutes, however we never know the time or duration of a power outage. At Pacific Fertility Center, we remain well rehearsed and prepared, just in case it happens on the busiest morning of the year.