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Chromosomal AbnormalitiesAn Explanation of the Predominant Cause of Miscarriage
Chromosomal abnormality, the leading cause of miscarriage, is responsible for about half of all miscarriages.
Proper development of a baby depends on the number and structure of microscopic chromosomes. Scientists have identified many abnormalities that occur in these important carriers of our genetic information. Since development relies on the chromosomes, chromosomal abnormalities often result in miscarriage. Though scientists have identified many abnormalities, they are not yet able to determine their cause. Normal Cells and ChromosomesOur body is made up of tiny cells, which are constantly replenishing. The chromosomes, which sit inside the nucleus (center) of the cell, are the structures that carry the genetic information that determines each of our individual characteristics from hair color to body structure. There are 46 chromosomes in most cells. The cells of the male sperm and the female egg are unique in their number of chromosomes. At the time of fertilization, they each generally contain 23. Thus, when fertilization occurs, the sperm and egg share their genetic information, giving the resulting embryo 46 chromosomes per cell. Random Abnormalities Which May Cause MiscarriageAn error can occur in the maternal or paternal reproductive cells leaving the sperm or egg cell with too many chromosomes or too few. The resulting fertilized cell will have aneuploidy, the most common cause of miscarriage, in which there is an extra or missing chromosome in one or more of the individual pairs. Such abnormalities include:
Rarely, whole sets of chromosomes are duplicated, resulting in a polyploidy such as:
An additional condition within each of these abnormalities may occur, called mosaicism, in which the cells are not all the same. For example, some cells may have the normal 46 chromosomes, while other cells have one of the random abnormalities. Structural Abnormalities Which May Cause MiscarriageAbnormalities may also exist in the structure of the chromosomes. Parents who are carriers of structural abnormalities have a higher risk of miscarriage since the misplaced genetic information may not divide properly into the reproductive cells. Some of the more common types of structural abnormalities include:
Fetal KaryotypeSince the chromosomes carry the genetic information which triggers our individual development, errors in the chromosomes generally lead to abnormal development. These abnormalities are often so severe that the baby is incompatible with life. Thus, many chromosomal abnormalities end in miscarriage. Often, this occurs very early in the pregnancy. However, if there is enough fetal material to collect from a miscarriage, a karyotype can be performed to determine if such an abnormality existed. If a karyotype reveals a numerical abnormality, it is most likely random. There is usually no increased risk of miscarriage in successive pregnancies, with the exception of trisomy (which has been linked to maternal age). Parental KaryotypeIf, however, a fetal karyotype reveals a structural abnormality, a parental karyotype should be performed to determine or rule out a hereditary condition. Those who carry structural abnormalities should seek genetic counseling to determine the risks involved with future pregnancies. Patients with hereditary abnormalities have a higher risk of miscarriage and infertility, though many are able to have healthy children.
The copyright of the article Chromosomal Abnormalities in Infertility Causes is owned by Kristen O'Hara. Permission to republish Chromosomal Abnormalities in print or online must be granted by the author in writing.
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