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    edited by Alice D. Domar, Denny Sakkas, Thomas L. Toth.
    "Most chromosomal abnormalities are incompatible with life, but a small minority of them leads to normal development and lifespan (e.g., balanced Robertsonian translocations), while others, although life-compatible, have appreciable effects on the individual's phenotype (e.g., sexual chromosomes imbalances). Because of their compatibility with life, some aneuploidies may be present in the karyotype of individuals in reproductive age and therefore be transmitted to their offspring. The presence of a balanced or unbalanced translocation in the oocyte or spermatozoon that will form the embryo will determine embryo and fetus' karyotype (normal or abnormal) for that chromosome. The ability to evaluate the presence of structural rearrangements in individuals looking to conceive a baby would determine whether they require ART (and screening of the specific condition in embryos generated through IVF) or if they are not at risk for that determined condition. In this case, the use of ARTs will drastically reduce the chance of miscarriage, fetal death, abnormal conception, and birth defects. Age-related chromosomal conditions are not inheritable. They are caused by defects in the chromosomal set of germinal cells due to various reasons. The most common one is the accumulation of errors in the meiotic machinery, which results in a significantly inefficient process of germinal cell maturation during meiosis. This defective process is significantly more common in females than males due to the lengthy oocyte maturation progression[2]. According to standard scientific evidence, the number of female germinal cells is determined at birth and from this point in time they suspend their maturational process at an early stage of the first meiosis (dictyotene), which resumes during ovulation. There is solid evidence that the incidence of aneuploidy in embryos generated by women of advanced maternal age is significantly higher than in younger patients. This suggests that the longer the oocytes remain in this suspended maturational state, the higher the chance that the meiotic machinery accumulates defects and is unable to complete the process without resulting in the formation of chromosomal abnormalities. This defective process impacts the ability of females of advanced maternal age to naturally conceive a healthy baby. Since the occurrence of these chromosomal defects is not hereditary, ECS programs cannot precisely identify the risk of an individual to generate chromosomally abnormal gametes or embryos. The only effective strategies to assess the presence of nonhereditary chromosomal abnormalities in embryos and fetuses remain preimplantation and prenatal genetic testing"-- Provided by publisher.
    Digital Access  Cambridge 2020