What risk of chromosomal abnormality appears as women get older?
The risk of chromosomal abnormalities increases with the age of the mother. This is due to ageing of the ovarian reserve, which is expressed as a higher risk of the eggs distributing the chromosomes to the daughter cells incorrectly leading to embryos with extra or missing chromosomes.
Most of the embryos with an incorrect number of chromosomes end their development before implantation or in the first trimester of pregnancy. In short, most of these embryos either do not lead to pregnancy or lead to spontaneous miscarriage. Thus, the possibility of a full-term, healthy is reduced from the age of 36 and as the age of the mother advances.
A small percentage of these chromosomally altered embryos are compatible with life. The risk of having a child affected by some chromosomal anomaly in the population with infertility problems is:
% altered embryos*
*Estimated data from the Embryonic Medicine
Why does the advanced age of the mother increase the risk of chromosomal alterations?
Women are born with a set number of eggs that gradually disappear by a phenomenon that is called atresia, so that on reaching puberty around 300,000 eggs remain in the ovaries. In each menstrual cycle, one egg will develop and another 1,000 will be lost. In this way, at the age of 35, around 10% of the eggs will remain. The fewer oocytes remain, the lower their quality. It is common for a woman aged 38-40 to have already exhausted the reserve of eggs capable of leading to a healthy child.
The oocytes are the only cells in women that have 23 chromosomes, i.e. half of what the rest of the cells have. For this, it is necessary that during formation of the egg the 46 chromosomes are placed face to face so that they can separate by undoing the filaments joining them and leaving 23 (this process is called meiosis). But the passage of time causes alterations in this process and sometimes extra chromosomes may remain (if it is the 21 this will lead to Down’s Syndrome) or some may be lost, causing reproductive failure.
In these cases it is necessary to study these embryos to be able to identify those that are chromosomally normal. This is carried out by an In Vitro Fertilisation cycle with Preimplantation GeneticTest.