In women under 35 four in ten embryos are expected to be genetically abnormal. After that age, gradually, more and more embryos are genetically abnormal reaching to nearly all at the age of 45
The most significant single major factor that substantially influences IVF success is maternal/oocyte age. This has been evident from long time ago, as natural pregnancy rates decline with increasing maternal age. In IVF, success rates also begin to decline after maternal age of 35 years. This is followed by a steep decline after its 40s and approaches to a low single digit around 45 years. Miscarriages also increase sharply after 40s. Emphatically, in egg donation the success rate is constantly high across maternal ages since the oocytes come from young, under 35 year old donors.
Such clear clinical evidence is supported by preimplantation genetic screening (PGS). The evolution of molecular techniques has made it feasible to determine embryo cell euploidy before embryo transfer. One or two cells (blastomers) are surgically removed from a day 3 embryo or a small number of cells of a day 5 embryo (blastocyst) and are sent for chromosomal copy number determination. Recent techniques can detect all 24 chromosomal copy numbers making genetic screening more accurate.
In 2016, Z.P .Demco, et al. published an important scientific paper on PGS where they reported screening on 37711 embryos from different IVF centers. The mean percentage of embryos with normal chromosome numbers (euploid) was about 60 %, steady from 25 to 35 years of maternal age. But after 35 years there was a steep decline of the percentage of euploid embryos, reaching a small single digit number and frequently zero at the age of 45. These are very important numbers to remember when we run an IVF cycle. Objectively, the IVF success rate will inevitably be in proximity of these numbers for certain maternal/oocyte ages.
This is a so-called genetic bottleneck that restricts, by default, IVF results
We can otherwise say that in women under 35 four in ten embryos are expected to be genetically abnormal. After that age, gradually, more and more embryos are genetically abnormal reaching to nearly all at the age of 45. Normally even more, unknown numbers, embryos may have additional minor genetic problems. All these embryos cannot end up in live births. This is a so-called “genetic bottleneck” that restricts, by default, IVF results. This bottleneck is common and inevitable to all humans. We must take this into consideration when we explain IVF failures and discuss treatment expectations. Therefore the best approaches is to acknowledge and accept it and plan the whole infertility therapy and IVF process accordingly