Blastocysts

Pregnancy rates using blastocysts
Pregnancy success rates at Eugonia Unit following culture and transfer of blastocysts are over 80% per embryo transfer for women of all ages. More specifically, for women <35 years of age, the positive pregnancy test has reached an impressive 88% per embryo transfer over the last couple of years (2010-2011).  Pregnancy rates for women 35-39 years of age have also increased (72%), as well as for women over 40 years of age (56%).
See our pregnancy rates

Blastocyst culture

The term blastocyst describes a certain stage of embryo development, after 5-6 days of culture.

Expanded blastocyst.

Expanded blastocyst.

Theoretically, growth to the blastocyst stage is an indication of normal embryo development. In addition, it has been proven that embryos reaching the stage of hatching blastocyst have approximately a two-fold increase of implantation chances. The fully grown blastocyst is characterized by expansion, thinning of the zona pellucida and the accumulation of fluid among the cells. At this stage, the embryo contains 60-120 cells that form two distinct groups. The outer cell mass (trophoblast) that will give rise to the placenta, and the inner cell mass that will form the embryo.

The next stage of development is the hatching of the blastocyst from the zona pellucida. This is achieved through pressure on the zona from the expanding embryo and secretion of zona-digesting enzymes. This results in the rupture of the zona and the hatching of the blastocyst for the resulting opening. It is believed that hatching may be a mechanism of twinning; if the embryo is separated into two during hatching it is then possible for them to regenerate the missing cells and to develop as two different organisms (monozygotic twins) that share the same gender and genetic material.

Blastocyst in advancede hatching stage (EUGONIA Archives).

Blastocyst in advanced hatching stage (EUGONIA Archives).

Blastocyst grading

For blastocysts there is a different grading system in place than the one for day 2 and day 3 embryos. This grading system is based on the combined assessment of the different characteristics of a blastocyst which are the degree of expansion, the progression of hatching and the quality of the inner cell mass and the trophoectoderm.

•    Development-expansion of the blastocyst (stages 1 to 6):

Stage 1: early blastocyst

Stage 2: blastocyst

Stage 3: full blastocyst

Stage 4: expanded blastocyst

Stage 5: hatching blastocyst

Stage 6: fully hatched blastocyst

•    Number of inner mass cells (Grades Α, Β, C)
•    Number of trophoectoderm cells (Grades Α, Β, C)

Thus, on day 5, the ideal blastocyst is rated as 4AA (expanded blastocyst with excellent inner cell mass and trophoectoderm), whilst on day 6 the ideal blastocyst is rated as 5AA or 6AA (hatching or fully hatched blastocyst with excellent inner cell mass and trophoectoderm).

 

Blastocysts

 

The process of blastocyst transfer (5th or 6th day following egg collection) is similar to the embryo transfer on day 2 or 3, with the only difference being the number of the transferred embryos. Up to 3 embryos are transferred on day 2 and 3, while only one or two  blastocyst are selected transfer.
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Blastocyst culture leads to increased pregnancy rates

Blastocyst culture offers a strong selection method of the best embryos for transfer. It is already know that not all embryos can reach the blastocyst stage during culture in the laboratory. At Eugonia Unit, in average, 50% of fertilized oocytes will reach the blastocyst stage. Thus, the embryos that reach the blastocyst stage on the 5th day of their culture have already proven their dynamic for further development and they have a higher chance of implantation.
Nonetheless, blastocyst culture requires the use of specially designed culture media and a modern laboratory with experienced embryologist and optimal culture conditions.

The advantages for blastocyst transfer include:

•    Better selection of the embryos that have the highest potential for transfer
•    Increased pregnancy rates
•    Improved synchronisation with the endometrium
•    The possibility of transferring 1 or 2 embryos (in comparison to 3 embryos that are usually transferred on day 3) and thus the reduction in multiple pregnancy rates
•    The chance of monitoring for ovarian hyperstimulation syndrome (OHSS) and a safer embryo transfer as long as severe OHSS has not developed
Blastocyst culture is not suggested in all cases, as the availability of enough good quality embryos is a necessary requirement. This culture method can be applied to women with polycystic ovaries that had many eggs collected, to women with an increased chance of developing severe OHSS, in cases of severe oligo-astheno-teratozoospermia or testicular biopsy, in cases of previously failed attempts (when transferring embryos of day 2 or day 3), in cases of preimplantation genetic diagnosis, etc.  
At Eugonia, there is a successful program of culture and transfer of  blastocysts, with specific internationally acceptable criteria. The scientists, doctors and nurses of the Unit have the necessary knowledge and experience to inform and guide the patients in this matter.