Recent studies have shown a correlation between features in the process of egg cell division that may lead to chromosomal defects causing birth defects, including miscarriage. The finding applies especially to women over 40 who have an increased risk of miscarriage because of their age. The sperm and eggs each have half of the chromosomes needed for a health embryo. When the two combine during fertilization, the right number of chromosomes is present. These chromosomes are supposed to align during the cell division process. In sperm, the cell division cannot move forward unless the cells are properly aligned.
According to researchers, this may not always be true of egg cells. It may be possible for an egg cell to continue the division process even if the chromosomes are improperly aligned, leading to an abnormal number of chromosomes. Often offspring with an abnormal chromosome count die in the womb, but others are born with birth defects such as Down syndrome. The study indicated this is the case, but the question now is why do eggs not have to have all the chromosomes aligned properly to continue dividing.
One possibility is that age plays a part. Older women are known to have an increased risk of miscarriage and birth defects. The egg cells of older women were found to be more susceptible to this that those of younger women. It fact, it is suspected that by her 40s, around 50% of the eggs a woman produces are likely to be abnormal. For a woman in her 20s, this number is only around 10%. Really though, it does not matter how the issue occurs, whether from a change in hormones, protein loss, or some other factor, anything that disturbs the division is important. It is important to remember that not all abnormalities related to chromosomes are the same. There are some that lead to death, with about half of miscarriages being attributed to this.
However, some end in giving birth to living babies, including those that cause conditions such as Edwards’s syndrome, Down syndrome, and others. There are cases of births with birth defects caused by disorders in the sex chromosomes as well, with females only having one X chromosome instead of two, or males with one X and two Y chromosomes rather than one of each. These typically manifest in a milder manner.
It is unknown why the egg cells can behave this way, but one theory is that it is a much larger cell than others, which could cause it to not send signals as well. There is no solution to the issue as of yet, but with more and more women deciding to put off child bearing into later in life, it is become much more important to find a way to reduce the risk of chromosomal abnormalities that cause miscarriage and birth defects.