Blastocyst Culture And Transfer

The ultimate goal of Advance Reproductive Technologies is a normal single intrauterine pregnancy that ends with a uneventful delivery of a healthy infant. It has been a common practice among reproductive specialists to transfer more than one embryo at a time to increase the chances of establishing a pregnancy. However, the more embryos that are transferred, the more likely the couple may experience a multiple pregnancy. Under standard IVF culture conditions, only about 10 to 40% of fertilized eggs will progress to become a normal pregnancy. The challenge for the in vitro fertilization team is choosing the embryos most likely to result in a normal pregnancy. Accurate selection of these embryos enables the clinician to transfer fewer eggs, leading to fewer multiple pregnancies, and ultimately a higher pregnancy rate. Over the past several years, production of embryos in vitro conditions have improved, enabling us to culture embryos for up to five to seven days after retrieval. Normally, by this time the embryos have reached a stage of development called the blastocyst stage. This extended culture time enables nature to help select those embryos with the highest capacity to produce a pregnancy. Continued refinements and change offer greater opportunity for infertile couples. Blastocyst culture is the latest important step. " It is exciting for us to be able to offer our patients this promising state-of-the-art technique, as it provides us the ability to increase the odds of success versus risk in favor of couples when we assist them in their quest of parenthood." explains Dr. Ronald P. Wilbois, Medical Director of the Infertility & IVF Center.

What is Blastocyst Culture and Transfer? A blastocyst is an embryo that has developed for at least five days after fertilization and has divided into two different cell types. The surface cells, seen in the embryo, are called the trophectoderm and will eventually become the placenta. The inner cell mass will become the fetus. A healthy blastocyst should hatch from its "shell" (zona pellucida) by the end of six days, and within 24 hours after hatching it should begin to implant within the lining of the uterus. Since the advent of human IVF, embryos have been transferred to the uterus between 48-72 hours (Day-2 or Day-3 Transfer) after fertilization. However, it is known that under in-vivo conditions the embryos reach the uterine cavity around the end of the third day following fertilization. Two to three day old embryos usually are at the 4- to 8-cell stage. Since we cannot determine the viability of each embryo at this stage and given the high embryonic loss found during this period of time, it is common to replace a high number of embryos to compensate for those that may not implant. This practice yields adequate pregnancy rates. However, it often results in high order pregnancies. Because of the danger to the babies and the mother, in addition to the social and economic stress that the care and nursing of the newborns represent, high order pregnancies remain an unwanted serious obstetrical complication.

Keeping the embryos in culture for 5-6 days, instead of the shorter culture period, allows some of them to reach the blastocyst stage. Embryos at this stage of development have undergone a selective process where the weaker and unfit ones are selected out. Blastocyst stage embryos have a higher rate of pregnancy than the 2- or 3-day old embryos. This means that a blastocyst has a higher probability of implanting than those transferred at earlier stages. Therefore, Day-5 transfers (blastocysts) require less embryos per transfer. Usually two embryos are transferred as opposed to four to five Day-3 embryos. This dramatically reduces the probability of multiple pregnancy and in some cases day 5 transfers offer higher pregnancy rates.

The Infertility & IVF Center’s experience in Blastocyst Culture.

Two important factors have limited the number of embryos that will develop to blastocysts. First, the inherent "health" of any embryo will dictate its ability to continue to grow and divide. Several eggs may have initially fertilized, but only a few will progress to the four-cell stage, fewer still to the eight-cell stage, and even fewer will develop into blastocysts. Simply put, this self selection can be viewed as "survival of the fittest". The second limiting factor in preventing continued growth of embryos in culture had been the culture systems themselves. As early as 1993, we started to cultivate embryos in vitro to the blastocyst stage. We understood well that the dynamic processes of embryo development required more than the static nature of the one size fits all culture media that had been used prior to this point. Don’t we all require changes in our diets according to our age? Embryonic life could not be different from the extrauterine life. Therefore, from the beginning, we started the use of what today is called Sequential Media. "We understood that before the embryo metabolic activity takes over, they utilize the maternal nutrients stored in their cytoplasm. Therefore, we used a simple medium that would facilitate their development in vitro during their first 3 days in culture. Followed by culture for two additional days in a more complex medium that would support their development. Therefore, From the oocyte harvest onward, the embryos are exposed to specific media designed to meet the nutritional requirements of each stage of development." Says Dr. Jose J. Hernandez , Laboratory Director at the Infertility & IVF Center.

Refinements in technique promises to maximize safety and success rates.

Blastocyst culture and transfer is a new important technique that maximizes pregnancy rates while minimizing the risk of multiple pregnancy. The ability to grow embryos for five days to the blastocyst stage of development in the laboratory, rather than the traditional three days, allows clinicians to determine with greater certainty which embryos are really the "best" in terms of their potential for implantation. Consequently, blastocyst culture makes it possible to select the best one or two blastocysts vs. four or five early embryos to transfer back to the mother. This reduces the occurrence of potentially risky multiple births. "Infertility institutions like The Infertility & IVF Center constantly are looking for alternatives to improve IVF success rates through the steady refinements of clinical and laboratory techniques. Blastocyst culture and the new generation of embryo transfer catheters have played an important role in our impressive pregnancy success rates" explains Dr. Ronald P. Wilbois, Medical Director.

The Benefits of Blastocyst Transfer in Detail.

Let’s use a hypothetical case to illustrate our point. A patient has 13 oocytes harvested. With our current rates of fertilization, about 10 will become embryos (80%). At this point, it is not possible to determine which of these 10 are most likely to implant and develop into a baby. By Day Three, 7 of the 10 embryos may be developing into healthy 4- to 8-Cell embryos. The others may have slowed or stopped their development and their prognosis is not favorable. In this example, we are left with seven embryos that still look like they may have excellent potential. However, we cannot determine based on their appearance which ones are the best to transfer on day 3 after harvest. Further culture for two additional days in the blastocyst culture medium allows the natural selective process to continue. Thus, after 5 days of growth in the laboratory, only 4 or 5 of the original ten embryos may remain viable. We now know the best embryos to transfer. Embryos transferred at the blastocyst stage have made it through key developmental processes and typically offer a greater chance of implanting. Without compromising pregnancy rates, we need only return 1 or 2 blastocysts to the mother instead of the typical 4 to 5 less developed embryos that would be transferred on day 3. In fact, pregnancy rates in the group using blastocyst transfer may even be higher because the uterine lining is more receptive to the advanced embryos. In addition, if there are more than two available at the time of transfer, the remaining blastocysts may be cryopreserved for future use.

Can we use blastocyst culture and transfer for everyone?

Bringing the example above, patients who have less than four embryos developing normally by 48 hours after fertilization have no advantage using blastocyst culture, since little is to be gained in further embryo self selection. The blastocyst culture conditions do not improve the health or viability of an individual embryo which is not otherwise able to develop for 5 days in vitro and then implant; rather it allows embryos capable of sustained growth to continue in culture and reach their maximum inherent capability. There are currently many unresolved issues regarding blastocyst transfer. Blastocyst transfer has a number of risks, and accordingly, is not appropriate for every couple. In a small percentage of patients, none of the embryos develop to the blastocyst stage and gradually degenerate. This results in a complete loss of all embryos. There are many other unanswered questions. Will blastocyst transfer improve pregnancy rates for patients with specific conditions, such as age, clinical history, etc but not for others? Is there a combination of factors (number of embryos for transfer and their inherent quality) to consider to achieve an acceptable pregnancy rate. Which patients are the most appropriate for blastocyst transfer?

Our Results with Blastocyst Transfer.

The transfer of high-grade blastocysts has resulted in implantation rates between 40% and 50%. With the transfer of only two blastocyst embryos, pregnancy rates as high as 80% have resulted. These high implantation and pregnancy rates are due, in large part, to nature's selection of those embryos that have the highest chances of producing a pregnancy.

Our criteria to choose Day-3 vs Day-5 (Blastocyst transfer).

Allowing the embryos to develop an additional two days in the laboratory gives us more discriminatory power to select the embryos with the highest developmental potential. In addition, replacing the embryos five to six days after fertilization allows the embryos to arrive in the uterus at a more physiologic time (with natural conception the embryo does not implant until about six days after fertilization). Blastocyst transfer may be of particular benefit for patients who develop many good quality embryos and want to limit their risk of a multiple pregnancy by transferring fewer embryos with higher potential for implantation. The decision to perform blastocyst culture and transfer is based on several factors including patient age, the number of eggs retrieved, previous IVF success, and perhaps most important, the embryo grade and cell count on day 2 of culture. We feel blastocyst culture and transfer has significant advantages for younger patients, egg recipients who receive eggs from younger donors, high responders (many eggs retrieved), or patients with previous IVF success. We encourage you to discuss the possibility of blastocyst transfer with your infertility team.

The risks of blastocyst transfer.

A significant potential risk when planning a blastocyst transfer is that none of the embryos may develop to the blastocyst stage. About 40% of the fertilized oocytes should develop to the blastocyst stage. However, in certain cases embryo development is severely compromised and there would be no embryos to transfer. In order to limit this risk, blastocyst transfers will only be performed in patients under 40 years of age or patients who are recipients of our oocyte donation program. Candidates for blastocyst transfer will be scheduled for an embryo transfer five days after egg retrieval. The embryos will be evaluated by the IVF laboratory staff on the morning of the second day after egg retrieval. If there are less than four high quality embryos, the patient will be called and the transfer rescheduled for Day-3. If no embryos have reached the blastocyte stage five days after egg retrieval, the embryo transfer will be rescheduled for the following day (six days after egg retrieval). If there are no blastocysts on day 6 after the egg retrieval, no transfer will be performed.

Summary.

We are now offering the therapeutic benefits of Blastocyst Transfer. By extending the time period embryos are in culture to 5-6 days, we have:

1. Minimized the risk of multiple pregnancy, thereby avoiding the need for fetal reduction or the undesirable results associated with higher order multiple pregnancies.

2.  Increased embryo implantation rates.

3.  Improved the selection of viable embryos for transfer.

4.  Created improved opportunities for preimplantation genetic diagnosis.

5.  Achieved high pregnancy rates with fewer embryos transferred

Together, the medical team and the couple carefully weigh influencing factors (age, health, embryo quality, donor eggs) to predetermine a reasonable number of embryos for transfer. Unfortunately, it is difficult to accurately predict which embryos will implant. By increasing the time embryos develop in culture we provide a more sensitive criterion from which to select functionally competent embryos that have a better chance of implanting. The most important benefit of blastocyst culture and transfer is the reduction of high order multiple births that can result from in vitro fertilization. This means that various obstetrical complications that may arise from multiple pregnancies can be minimized. It is especially important in helping patients avoid having to make the difficult personal and ethical decisions regarding selective reduction. We are excited to be able to offer this option to our patients.