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Inherited Disorders and Birth Defects

What does an extra marker in an amnio mean?

07/07/2008

Question:

We just had an amnio and it showed an extra marker. They tested our blood and we did not have it. They say that it is not affecting all cells (most are normal). Is there a chance everything is okay or is there definitely a defect? Are there any other tests we can have performed? Thank you.

Answer:

While not common, small markers (called supernumerary markers) are seen in about 1 per 1000 prenatal karyotypes (the diagram of the baby's chromosomes). They are often seen in a mosaic form (that means that only some cells have the marker, the others do not), which sounds like your situation. Depending on what part of the chromosome the marker came from, it can lead to no effect in the baby or could cause birth defects.

Thus in your case, there is definitely a chance that everything is OK, but there is also a chance that the marker could mean that there are birth defects present. Usually the genetics laboratory uses a number of different lab techniques that can help identify where the marker came from and thus provide some additional information about what this might mean for the pregnancy.

Having a comprehensive ultrasound looking for birth defects may also give you more information. If you have not already done so, I would highly recommend that you speak to a genetic counselor or geneticist. They would be able to provide you with additional information based on the findings from the karyotype, as well as to see what additional studies are being done in the laboratory to identify where the marker may have come from. You can locate a genetics center near you at the National Society of Genetic Counselors website listed below.

Related Resources:

National Society of Genetic Counselors Resource Center

For more information:

Go to the Inherited Disorders and Birth Defects health topic, where you can:

Response by:

Anne   Matthews, RN, PhD Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University