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Inherited Disorders and Birth Defects

Chromosome 13 inversion



I`m 13 weeks pregnant and just got my CVS test results back. It came back w/ an inversion to the 13th chromosome. (the para type). I`ve read that if either my husband or I have the "flipped" chromosome that the baby is fine - but if neither of us has it than the risks are great for birth defects. Is this correct? We are giving blood tomorrow to determine if either of us has that gene.


An inversion happens when a chromosome breaks in two places and the area between the two breaks is inverted (turned around), and then reinserted. The breaks then unite to the rest of the chromosome.

Each chromosome has a p arm - the short arm and a q arm - the long arm. In between the p arm and q arm is the center or centromere. A paracentric inversion is an inversion that happens in either the short arm or the long arm, but does not include the centromere (the center of the chromosome.

If all of the chromosomal material is present and functioning, just rearranged, then that person is called a balanced translocation carrier. However, if some of the chromosomal material is lost or duplicated when the chromosomes breaks and an inversion takes place – then there is extra and / or missing information that can lead to birth defects and cognitive problems such as learning disabilities and mental retardation.

If a pregnancy has a chromosomal inversion and one of the parents has the same inversion - these can be compared to each other. In this case, there is a high likelihood that the child will be like the parent - a balanced translocation carrier and no problems due to the inversion. If the inversion is only in the pregnancy and not the parents, there is a very small chance that some of the genetic material could have been lost or duplicated. This could lead to birth defects or other problems. Chromosome analysis is very accurate, but if the lost or duplicated chromosome material is extremely small (submicroscopic) or disrupted a gene, there could be an unbalanced rearrangement in the baby.

If you have not already done so, I would recommend that your doctor refer you to a geneticist or genetic counselor who would be able to give you more information for your specific situation.

You can locate a genetics center near you at the website 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