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Mostly because we’re born with all the eggs we’ll ever have. You actually had the most eggs you’ll ever have three months before you were born and you started losing them already before you’re even born so by the time you get to wanting to start a family at 30 or 35 or 40, those eggs have been sitting in your body all of that time. They’ve been subjected to everything that you’ve done in your life up until then. If you’ve starved yourself, overeaten, worked out really hard, not worked out at all, binge drinking all the way through your twenties -whatever – all sorts of different things can impact how the environment that those eggs are in throughout that time. So by the time you get to starting a family, those eggs have been subjected to all of that and all of that will impact the egg quality. Also things break down in the eggs over that time so by the time we’re 35, we have fewer mitochondria and they function less well. The mitochondria are the part of the egg that are really responsible for how resilient the egg is going to be through those first three days of development – from fertilization, through to day three. It’s really important that we support our mitochondria as much as we can.
Answer from:
This is a central question in order to better understand biology aging for the oocyte. When considering oocyte quality we should always take into account that oocytes are sensitive cells, which are produced during fetal life and do not have the ability of self-renewal. This means that everything we do in our daily life could negatively impact oocyte quality and thus our reproductive potential. It is widely accepted that as maternal age increases oocyte quality is progressively compromised. This reduction regarding both oocyte quality and ovarian reserve starts approximately after 30 years of age, becomes more intense after 35 and peaks after 40. It is a natural process where the cellular and the molecular mechanisms regulating proper oocyte functionality are compromised in several levels. Thus, errors are observed mainly with regards to the mechanisms regulating chromosome segregation during the meiotic divisions. Meiosis is a special category of cell division, which takes place during gamete production in both females and males. Errors in meiosis affect the number of chromosomes for gametes and subsequently for embryos, finally leading to aneuploidy. Thus, women of advanced age have an increased risk of embryo aneuploidy such as trisomy 21, which is widely known as Down syndrome. Apart from errors during meiosis, oocyte aging can also cause telomere shortening. Telomeres constitute short DNA sequences found at the end chromosomes which protect the genetic information from damage. As maternal age increases telomere shortening is observed, making DNA more sensitive to damage. In the same context, during our lifespan several external and internal factors can cause damage to oocyte DNA, namely mutations. Oocytes are equipped with a perplexing network of molecular factors which can successfully locate and repair these damages. However, as maternal age increases, the efficiency of these repair mechanisms is significantly impaired resulting in mutation accumulation. These mutations negatively impact both oocyte quality and its competence. Oocyte competence refers to the ability of an oocyte to successfully support embryo development. Moreover, aged oocytes are characterized by impaired mitochondria functionality. Mitochondria are small subcellular compartments serving as the ‘’powerhouse’’ of a cell, producing chemical energy required for proper oocyte functionality. Moreover, mitochondria are able to protect oocytes from the damaging effects of reactive oxygen species, which are produced from several biological and environmental processes. Thus, aged oocytes are very sensitive to oxidative stress and cannot successfully support early embryo development. In summary, oocyte aging is a normal, albeit complex biological process which is associated with impaired embryo development, embryo aneuploidy and adverse obstetrical, perinatal and neonatal outcome. Despite the fact that we cannot avoid or reverse oocyte aging, we can adopt healthy lifestyle behaviors in order to improve aging-related deterioration of oocyte quality.
