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There is an equation that we can use to illustrate the implantation process:
Patients that fail IVF will often ask;
Sometimes, after repeated failure to implant any embryos with IVF, women will say;
Although this could be logical. It does not fit with the science. When IVF does not work after numerous attempts – switching the uterus is not likely to result in success. However, the egg donation experience teaches us that switching to eggs from a young egg donor would be very likely to be successful.
This tells us that the problem is not the uterus but is the egg quality. Therefore, it works when we switch to different eggs from a young woman.
Some animal species have much higher implantation rates per embryo transferred than humans do. Human IVF is not as efficient due to the relative weakness of the human egg as compared to those animal species.
This is not to say that the sperm and the uterus are not sometimes contributing factors in the IVF success equation. However, the sperm and the uterus are relatively minor factors as compared to the major factor of egg quality.
We know that one of the major factors contributing to in vitro fertilization failure is the high rate of chromosomal abnormalities in human embryos.
As women age the incidence of chromosomal abnormalities in mature eggs increases significantly. Studies have shown that starting in the early 30s, the rate of chromosomal abnormalities in human eggs (and therefore in human embryos) starts to increase significantly.
The rate continues to increase with advancing female age so that by the mid-40s a very high percentage of human embryos are chromosomally abnormal (over 75%).
It is believed that this is mainly due to problems with the spindle apparatus in the egg nucleus. The spindle is involved with properly lining up and segregating the chromosomes as the egg matures at the time of ovulation.
Older eggs have an inefficient spindle apparatus that does not line up the chromosome pairs properly and “mistakes” are made when splitting pairs of chromosomes. This leads to eggs that do not have the proper balance of 23 chromosomes – and will result in a chromosomally abnormal embryo if fertilized.
It has been shown that about 1% to 2% of human sperm are chromosomally abnormal on the average – as compared to about 20% to 90% of human eggs (depending on female age).
PGS – preimplantation genetic screening can be done on embryos prior to transfer to evaluate chromosomal competence.
Culled from http://www.advancedfertility.com/ivf-implantation-failure.htm
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