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by Walsh B

Risk Factors for Chromosomal Abnormalities

A risk factor is something that increases your likelihood of getting a disease or condition.
It is possible to develop a chromosomal abnormality with or without the risk factors listed below. However, the more risk factors you have, the greater your likelihood of having a baby that develops a chromosomal abnormality. Talk to your doctor about how you can reduce your risk.


The leading cause of chromosomal abnormality is the mother’s age. The likelihood increases as the mother’s age increase. However, more babies are born to younger women, so more babies with a chromosomal abnormality are born to younger women. The actual number of chromosomal abnormalities passed on is difficult to determine because most result in miscarriages early in the pregnancy.
Maternal Age Risk of Any Chromosomal Abnormality Risk of Downs Syndrome
15-24 1/500 1/1500
25-29 1/385 1/1100
35 1/178 1/350
40 1/63 1/100
45 1/18 1/25
These statistics only account for live births.

Medical Conditions

If you have already had a child affected by a chromosomal abnormality, you are at increased risk for passing along another chromosomal abnormality.
If you and your partner have experienced at least 2 spontaneous abortions, you should talk to your doctor about conducting an investigation of your chromosomes. This investigation comes back normal 95% of the time. If the results are not normal, you and your partner should meet with a human geneticist.

Living Environment

A study published in February 2005, showed that prenatal exposure to combustion-related urban air pollutants alters the structure of chromosomes of babies in the womb. This is the first study to show that environmental exposure during pregnancy to such pollutants can cause a modest but significant increase in chromosomal abnormalities in fetal tissues.


Chromosome abnormalities. National Human Genome Research Institute website. Available at: http://www.genome.gov/11508982. Updated January 6, 2016. Accessed June 6, 2016.
Study: prenatal exposure to air pollutants causes genetic alterations. Columbia University website. Available at: http://www.columbia.edu/cu/news/05/02/pollution%5Fpregnacy.html. Published February 22, 2005. Accessed June 6, 2016.

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