Findings from new research may finally resolve, and potentially provide answers, as to why older women have higher incidences of miscarriage and have babies with chromosomal abnormalities.
Female fertility declines rapidly after the age of 37 -- with women over 42 having only a five per cent chance of having a baby without fertility treatment. The problem is that as a woman ages, her eggs also age -- increasing the chances of chromosomal abnormalities. This leads to an increase in conditions such as Down's syndrome, where the egg has three copies of chromosome 21. However most chromosomal abnormalities in eggs lead to embryos that either fail to implant in the womb, or miscarry soon after implantation. In women over 40 most miscarriages are caused by the wrong number of chromosomes being present in the egg.
In a paper published in Nature Communications, researchers reveal a fault in how the egg controls the levels of a protein called securin. In the final stages of egg development just before ovulation, it undergoes two specialized cell divisions known as meiosis I and meiosis II. Securin is important for both divisions but in old eggs, it appears that there is insufficient securin remaining to ensure meiosis II takes place normally.
Most chromosome abnormalities occur in the first egg division (meiosis I) but it is known that a substantial number of abnormalities also occur during meiosis II. In these older women the chromosomes in their eggs start to fall apart because there is insufficient securin to control the process. Authors found that over-expression of securin protects against the age-related increase chromatin abnormalities.
The discovery opens the way to improving an older woman's chances of having eggs with fewer chromosomal abnormalities through regulating the processes that control securin levels in the two divisions of the egg or controlling the protein that securin regulates (a protein called separase).
The research team is working with Monash IVF to improve in vitro maturation and identify new targets that may be able to better control prevent the degradation of Securin, according the senior author.
Why older women have increased incidence of chromosomal abnormalities and miscarriages
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