Through new knowledge over the embryo physiology, better and more suitable culture medium have been developed in which the in vitro culture can develop up to the blastocyst stage. These new medium minimise the risk of loosing viable embryos as was often seen in the past in prolonged in vitro cultures.
As the metabolism of the embryo varies before and after compaction, different medium are taken into consideration.
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Better synchronization between uterus and embryo development. Compared to the in vivo situation, embryo transfer on day 2/ day 3 after follicle punction is at least 2 days too early.
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Selection of the best embryos: using these culture techniques those embryos with the best development potential can be transferred. Quite often the embryo genome is not activated, and the 4-8 cell stage is not passed. These cells can’t be identified as pathological when customary medium are used.
At this stage development may stop: due to genetic reasons, through apoptosis, the mothers age or influence from the father.
Patients with chromosome translocation can profit from the blastocyst transfer technique. Embryos with a special translocation don’t continue developing when they are left in culture mediums for longer periods. (Development-Arrest). Therefore, if the cells can stay in the culture medium up to the blastocyst stage, we have the possibility of selecting an active embryo for transfer, thus enhancing the chance of the birth of a healthy child.
In regards to these aspects, a blasocyst transfer is advisable for women over 38yrs. of age. The risk of aneuplodie (varying numbers of chromosomes) increases with the age of the woman, and embryos with aneuplodien tend to stop developing in the first few days.
When one or two embryos in the blastocyst stage are transferred, there is a higher implantation rate. Multiple pregnancies (>2 children pro pregnancy) can be avoided. The chance of tubal pregnancies can also be reduced because the uter-tubare transition on day 5 after follicle punction, physiologically prevents the blastocyst from slipping back into the fallopian tube.
Another big advantage of transfer on day 5, is that there are diminishing uterine contractions after this period. Therefore there is a better chance that the embryos that have been placed back in the uterus won’t be expelled!
This has been proved by a reliable scientific study in which the uterine contractions were measured and recorded.
(see- Uterine contractility decreases at the time of blastocyst transfers.)
Disadvantages
As only about 40% of all embryos develop to the blastocyst stage, (this is due to many different factors, some unknown) and the development to this stage can’ be predicted, there is the risk that when less than 5 egg cells are available, (even when fertilized) that they can’t be transferred in vitro because none of them have reached the blastocyst stage.
The fewer the number of eggs available at follicle punction, the less chance there is that at least one or two embryos develop to the blastocyst stage.
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It is also necessary that the embryos develop quickly enough to the blastocyst stage. (at least one early blastocyst should be present on day 5)
=> This means that: this method is applied at the present on patients with more then 5 egg cells, and especially on patients who have had repeated negative attempts of in vitro fertilization.
After analysing reports from previous experiences, we saw that when an average of 1.7 embryos were transferred in blastocyst stadium, that 56.2% of the pregnancy tests were positive. By 47.4% positive heart action was noted. Therefore in relation to one embryo in the blastocyst stage, an implantations rate of 27.4% pro embryo was achieved.
“Der Blastocystentransfer im Vergleich zum klassischen Embryo Transfer” : H Zech, N. Zech, P.Vanderzwalmen. In: Kinderwünsch: Möglichkeiten, Erfüllbarkeit und Machbarkeit in neuen Jahrtausend. Krause und Pachernegg – Verlag für Medizin 2000.
PS: This blastocyst-Culture-Technique is unfortunately not legal in Germany and Switzerland.