To fulfil their desire for having a child of their own many couples have to undergo fertility treatment including ovarian stimulation and subsequent fertilization of collected oocytes and the partner’s semen. The fusion of oocyte and sperm can be achieved either by a classical IVF (in vitro fertilization), that is to say oocytes and spermatozoa are added in a culture dish or when dealing with suboptimal sperm quality by “Intracytoplasmic Sperm Injection” (ICSI) or “Intracytoplasmic Morphologically Selected Sperm Injection” (IMSI).
Thereafter the fertilized oocytes stay in culture for 5 days (blastocyst - selection).
Why is it sensible to perform blastocyst - selection after fertility treatment?
Altogether only about 3 oocytes out of an average of 12 oocytes, produced each year by a woman having a regular menstrual cycle (an ovulation each month = 12 x ovulation a year) are capable to develop into a child after fertilization. Another 1 – 2 oocytes may lead to pregnancy but result in a miscarriage (abortion).
In theory almost all 12 oocytes (as well those, that do not lead to a pregnancy) are potent to develop up to day 3 of embryogenesis even when they have never met a sperm. This is referred to as parthenogenesis – can be triggered by an electrical impulse or other kinds of stimuli.
Only after that the oocyte realizes the lack of a sperm. The 1 – 2 egg cells that could lead to a pregnancy mostly show chromosomal abnormalities with an extra chromosome (as the most frequent are to be mentioned: trisomy 21, 13, 16 and 18). On the other hand there could also occur a lack of chromosomes (monosomies), which usually do not lead to a positive pregnancy test. Such chromosome abnormalities (aneuploidies) can be detected by means of the “Preimplantation-Genetic-Diagnosis”(PGD) or by examining both polar bodies (polar body = PB) of the oocyte.
Chromosomal abnormalities are more frequent with advanced maternal age, because the oocytes are also aging. This is comparable to an elastic band getting brittle after years and ripping at least, maybe sooner when being exposed to extreme environmental factors (e.g. sunlight [UV-radiation], frequent variations in temperature etc). What these factors do to the elastic band is comparable to what for instance tobacco smoking, an excessive way of life, hormonal disorders etc. can do to a female. Each chromosome is attached to such an elastic band and if it rips one/more chromosomes will remain in the oocyte, thus frequently provoking either a trisomy or a monosomy. Sometimes multiple chromosomes are affected, depending on how many elastic bands will rip and in which direction the ripped band will bounce to.
It has to be mentioned that in most of the cases there is no pregnancy achieved by oocytes with chromosomal abnormalities (negative pregnancy test), for they are showing multiple chromosome abnormalities or monosomies at the same time.
This doesn’t apply for “viable chromosomal abnormalities” such as trisomy 21, 13, 16 or 18 which occur more frequently connected to advanced maternal age. But even these cases, only rarely lead to live birth, for most of these pregnancies end in an early pregnancy loss (about gestation week 12 – 16, or often earlier about gestation week 4-6 (abortion rate > 98%).
That’s why, even under best conditions we cannot give a 100% guarantee for a viable pregnancy, but only try to perform selection of the most promising embryos. A sensible selection is only possible by observing embryo development up to day 5 (blastocyst stage) – sporadically at the utmost up to day 6 (exceeding day 6 the embryos need to be in the womb, thus it’s not possible to keep them in culture any longer). As we said before, oocytes that have never “seen” a sperm are able to continue development up to day 3, for the semen’s genom is activated step by step starting from day 3 and taking an active part in embryo development (= “Late Paternal Effect”). On day 3 parthenogenetically activated oocytes (i.e. those which have never been fertilized by a sperm) may look as nice as fertilized oocytes. On day 5, referred to as blastocyst stage, they are quite simply no longer there, because development cannot continue without semen. (development could also stop due to chromosomal disorders- exceptions as we said before are e.g. trisomy 21, 13, 16 or 18.
Therefore, based on an average of 12 collected oocytes we could achieve by means of fertility treatment, referred to as IVF, a pregnancy rate of 80% in a young woman considering an abortion rate of 5 – 10%. This corresponds to a “Baby Take Home Rate” (BHTR) of 70 – 75%. Transferring 2 blastocysts will increase the risk of a multiple pregnancy by 20 – 30% without considerably improving the pregnancy rate (possibly by 5 – 7% at the utmost).Thus in these cases we tend towards an elective “Single Embryo Transfer” (eSET) in order to make the wish for a baby come true. Please note that the chances of getting pregnant cannot be considerably increased by transferring 2 blastocysts, however the risk of multiple pregnancy rises significantly.
It does not only depend on the quantity of collected oocytes, but also on their quality. There are women producing only a few oocytes and the majority of them reach the blastocyst stage. Whereas there are women producing many more than 12 oocytes, however a similar number of blastocysts develop as in women with, say, 12 oocytes. This is only to be assessed after having performed blastocyst selection. Therefore, in any case we strongly recommend blastocyst selection.
Our new scientific research has led us to the following findings:
Performing blastocyst selection it may occur that after transferring one blastocyst into the womb, there are one or more remaining blastocysts in culture – for these are potential babies.
It goes without saying that we want to deep freeze (vitrification) these remaining blastocysts, for many couples wish to have a brother or sister for their child, or the first attempt wasn’t successful and these blastocysts could be used for another, this time, successful try.
With Dr. Pierre Vanderzwalmen, for a long time, we have got a pioneer in the field of vitrification of embryos on our team.
We were able to establish a new classification system about how to assess blastocysts after thawing in order to select the best one to be transferred into the womb. Hence the pregnancy rates can further be improved. It is our common goal to fulfil each couple’s wish to have a child of their own as early as the “first cycle”, if possible.
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