What Is It?
If a pregnancy ends after 20 weeks, it is not considered a miscarriage. The fetus gets delivered, and if the fetus is not living, the event is called a stillbirth.
Problems with fetal chromosomes account for approximately 50% of all miscarriages. Chromosomes are long strings of DNA, each containing thousands of genes. Genes, in turn provide the instructions for the proteins and other molecules that create, shape and govern our bodies and health.
In most cases, the abnormalities of chromosomes that caused a miscarriage do not reflect any abnormality in either parent. Instead they reflect problems that developed at the time the egg or sperm developed, or at the time when fertilization and early division of the fertilized egg took place. In these case, where the miscarriage is related to chromosomal abnormalities, many think of it as the body's way of ending a pregnancy that is not developing normally.
In some unusual circumstances, miscarriages can happen if there are problems with the internal structure of a woman's uterus or the function of her cervix.
Infections such as rubella (German measles) have been associated with miscarriage. This has led some to wonder if there are other infections that cause early pregnancy loss, but few links have been confirmed. Some experts have also suggested that hormonal imbalances can result in miscarriage, but identifying specific abnormalities has proven difficult.
In rare cases, a woman's immune system appears to react with the pregnancy tissue, resulting in miscarriage. Overall, immune system disorders seem to be responsible for very few miscarriages, but among women who have had three or more miscarriages in a row (recurrent miscarriage), immune-system disorders are responsible for 5% to 10% of these losses. One fairly common antibody problem that can lead to recurrent miscarriage is called "antiphospholipid antibody syndrome." Another example of an immune related issue associated with miscarriage is the production of antibodies that react to the thyroid gland (thyroperoxidase antibodies).
Having either type of antibody is unusual. But it may be more common when there have been several miscarriages (recurrent miscarriage). Testing for such antibodies after several miscarriages is often suggested. Treatment for the antibody disorders may decrease the risk of future miscarriage.
In many cases, no cause for a miscarriage is identified.
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