This is the most common reason for a miscarriage and is usually the result of a one-off genetic abnormality in the baby that is unlikely to recur. In other words nature is working according to the law of survival of the fittest. When the baby is abnormal it will try to stop that pregnancy continuing.
You and your partner each contribute 23 chromosomes to the baby, making 23 pairs in total. Each chromosome pair determines specific characteristics of your child and geneticists have given a number to each pair. For example, number 23 is the pair which determines the sex of the baby.
Only a small portion of chromosomal abnormalities are inherited and these can be screened. The others can occur before, during and after fertilisation, as the chromosomes divide. It is thought that up to 50 per cent of miscarriages can be due to a genetic abnormality.
The most common chromosomal abnormality diagnosed is where there are three chromosomes in the pair instead of two. Depending on which pair this happens to, it will give rise to a specific abnormality. Not all abnormalities always end in a miscarriage. For instance, Down’s Syndrome is caused by an extra chromosome on pair number 21 and for that reason is also called trisomy 21. It is thought that most trisomies are caused by an abnormal division in the egg which occurs before fertilisation.
This may explain why older women have always been thought to have a higher risk of having a Down’s Syndrome baby, since older women’s eggs are more likely to be abnormal. But the Down’s Syndrome Association claims that eight out of ten babies with Down’s Syndrome are born to mothers under the age of 35.The extra chromosome can also come from the man’s sperm. So, at the moment, scientists do not know for sure what causes Down’s Syndrome.
However, there are links between Down’s Syndrome and mineral deficiencies. For example, people with Down’s Syndrome children have lower levels of zinc and selenium compared with others of the same age. It has also been found that in Down’s Syndrome blood levels of the ‘antioxidant defense system’ enzymes (super-oxide dismutase and glutathione peroxidase) are over-produced. Both these enzymes are produced by the body to disarm free radicals. The building blocks for these enzymes include the minerals zinc and selenium.
Selenium is known to protect against chromosome (DNA) damage by protecting the body against toxins and pollutants, and future research may demonstrate the importance of prospective parents having good levels of this mineral in the months before conception when both sperm and eggs are maturing.
The idea that toxin damage could be implicated in Down’s has been borne out by a study in the wake of the Chernobyl nuclear disaster. Babies born nine months later showed a six-fold increase in cases of Down’s Syndrome. Studies on animals have also shown it is possible to damage the chromosomes by introducing a toxin.
So the opposite may also be true: that you can protect your chromosomes from damage by stopping your intake of all the toxins we have been talking about and making sure that you have enough antioxidants to fight unavoidable pollution (like traffic fumes).
Turner’s Syndrome
If one chromosome of the pair is missing the condition is called monosomy. The most common abnormality of this type is where one X (female chromosome) is missing from the sex pair (number 23).This condition is called Turner’s syndrome. It does not usually cause a miscarriage but the baby, which is always a girl, will have certain physical characteristics. She can have heart defects and fertility problems, because her ovaries may be absent or fail to develop and because of this she will have under-developed breasts. As she gets older, she will need hormone treatment and counseling.
Inherited Genetic Problems
This is a much less common reason for a miscarriage, and chromosome testing (karyotype analysis) would be recommended for both partners where couples have experienced recurrent miscarriages. One of the most common structural changes in chromosomes is translocation, where part of one chromosome comes away and reattaches to a different chromosome.
Some gene defects can cause miscarriages but it is more likely that the genetic problem will cause abnormalities in the baby, such as cystic fibrosis or muscular dystrophy.
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