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Miscarriages in the first trimester of pregnancy |
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What is a chromosome disorder and what is its significance? |
Miscarriages in the first trimester of pregnancy are relatively common, and occur in
approximately 20-25% of pregnancies. The causes of miscarriages are multiple,
and cover a range of factors associated both with the fetus and the mother. Fetal causes include
chromosome disorders and syndromes, non-chromosomal genetic disorders, and abnormal fetal development.
Maternal factors include chronic illnesses, viral infections during pregnancy, abnormalities of the uterus, etc.
There are also many factors that are as yet unknown.
Abnormal fetal chromosomal structure is one of the most common causes of miscarriage.
Usually this is a new occurrence arising in the fetus, but in a small number of cases it is the result
of a chromosomal problem in one of the parents. Here the parent carries a structural change in one
of his/her chromosomes in a balanced manner (a translocation or inversion). The parent is completely
healthy, because there is no change in the total amount of genetic material, but the fetus may receive an
unbalanced chromosomal complement (insertions or deletions of complete chromosome segments or whole chromosomes).
In some cases, the change causes a miscarriage.
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Because of this possibility, in cases of multiple miscarriages,
sometimes a sample of the fetus removed by curettage is sent to a genetic institute
for examination of the fetal chromosomal structure (karyotype).
This is performed only in cases of multiple miscarriages (more than 3).
In some cases the parents' karyotypes are also analyzed.
About 1% of women have 3 or more consecutive miscarriages and about 10% have 2 or more.
In cases of women who have recurrent miscarriages (three or more, although many physicians consider
two to be the borderline), it is important for both partners to undergo blood tests for chromosome
analysis in order to determine whether either of them
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carries a balanced structural change (translocation or another problem, such as
mosaicism, marker, etc.)
According to reports in the
literature, such changes are not rare, and in 5% of cases of recurrent miscarriage,
a balanced chromosome problem in a parent is identified. Such couples have a higher risk of having a fetus
with an unbalanced chromosome disorder in each additional pregnancy, and prenatal diagnosis should
be offered in each pregnancy in order to prevent the birth of an infant with a chromosome disorder
leading to defects or mental retardation.
It is important to consult one's physician in all cases of recurrent miscarriage.
A history of miscarriages in other family members and/or cases of intrauterine death and/or the
birth of an infant with defects is important, as the presence of these can mean an increased risk
for the couple concerned.
In addition, tests for excessive clotting tendency (blood clotting) should be carried out in
cases of recurrent miscarriage, especially if there is a history of intrauterine death or late
pregnancy loss. It is possible to test the mother for a genetic predisposition for an increased
blood clotting tendency, and if this is found, an anti-clotting drug such as aspirin, etc., is administered.
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