The Blastocyst culture and transfer procedure for In-Vitro Fertilization facilitates selection of the best quality embryos for transfer to the uterus of the mother. The concept of embryo quality is a very important one for couples experiencing infertility. With Blastocyst embryo transfer, we can transfer fewer embryos - reducing risks for multiple pregnancies - while keeping overall pregnancy rates high.
A Blastocyst is an embryo that has developed for five to seven days after fertilization. At this point the embryo has two different cell types and a central cavity. It has just started to differentiate. The surface cells- called the Trophectoderm, will become the Placenta, and the inner cells-called the inner cell mass, will become the Fetus. A healthy Blastocyst should begin hatching from its outer shell- called the Zona Pellucid, by the end of the sixth day. Within about 24 hours after hatching, it should begin to implant into the lining of the mother's uterus.
Blastocyst culturing is a technique to grow embryos beyond the 3rd day of culture. Typically we transfer embryos into the uterus, 3 days after the egg retrieval when the embryos generally are between 6-8 cells. When the embryos are cultured to day 5 they become round 120 cells which is known as blastocyst.
The natural process of embryo development begins with the fertilization of the egg in the outer aspect of the fallopian tube. As the newly formed embryo develops, it moves slowly towards the uterine cavity where it will ultimately implant. This process takes approximately 6-7 days. When the embryo reaches the "Blastocyst" stage, it is ready to implant.
Why should we consider Blastocyst transfer?
In certain patients, the advantage of Blastocyst culturing is to allow optimal selection of embryos for transfer, resulting in an increased implantation rate per embryo transferred. However, it is important to understand that this technology may not necessarily increase your chance for pregnancy. The main advantage is that fewer embryos may be transferred to eliminate the possibility of triplet pregnancies, while maintaining a high pregnancy rate.
Is it for everyone?
No. Generally speaking, this procedure should be limited to patients with excessive numbers of embryos (greater than 10) in which case further selection of embryos beyond the day 3 stage would be advantageous. As a general rule, patients under the age of 37 are candidates for this culturing technique. We do not recommend this procedure to older patients because the risk of having no Blastocyst embryos for transfer is too great.
What percentage of embryos will grow to the Blastocyst stage in culture?
For younger patients, up to 50% of all embryos will continue to grow to the Blastocyst stage. However, 10% of patients will not have an opportunity for embryo transfer due to the absence of Blastocyst development. As patients get older, fewer and fewer numbers of embryos are capable of developing in culture to the Blastocyst stage.
What are the risks of Blastocyst culturing?
There are two main concerns with Blastocyst culture:
- Some patients may have no embryos development to Blastocyst and thus lose the opportunity for a transfer.
- The number of embryos for freezing and the survival of embryos after thawing will decline, potentially lowering the overall pregnancy potential of a single stimulation/egg retrieval treatment cycle.
How do we know if we should seriously consider it?
If you are younger than 37 years old with a normal day 3 FSH level and have a strong desire to avoid triplet pregnancy, then you should seriously consider it. If you have an absolute reluctance to selective fetal reduction, then you have even more reason to consider Blastocyst culturing.
Are there any limitations to Blastocyst culturing?
Yes, if you have less than four, 8-cell quality embryos on the 3rd day of culture, we do not recommend proceeding with Blastocyst culturing even if you so desire it. With Blastocyst culturing, we are not able to freeze as many embryos because of poor embryo development to the Blastocyst stage. Also, there appears to an increased risk of identical twinning with Blastocyst culturing (including the possibility of conjoint twinning where the babies may be connected and share some organs). Fortunately, the risk of identical twinning is very low (<1%).
Would the embryos that arrest in culture prior to the Blastocyst stage have arrested in the uterus?
There is no possible way to completely know this answer. We believe that embryos that do not survive in culture would be less likely to survive or implant in the uterus.