B asked in HealthWomen's Health · 6 years ago

Why is down syndrome more common in older mothers?

I am writing an essay and I need to explain why it is more common. Is it a myth? Is it because the eggs are older? What causes it to be more common besides age?


And why would having older eggs cause it to be more common if that is the case?

3 Answers

  • 6 years ago
    Favourite answer

    What Is Down Syndrome?

    Down syndrome is one of the most common genetic birth defects. Usually, children born with the condition have some degree of mental retardation, as well as characteristic physical features. Many of these children also have other health problems.

    Each year in the U.S., approximately one in every 800 to 1,000 newborns has Down syndrome. This results in approximately 5,000 children born with Down syndrome each year.

    In the U.S. today, Down syndrome affects approximately 350,000 people. As many as 80% of adults with this condition reach age 55, and many live longer.

    The most common form of Down syndrome is often called "trisomy 21," because individuals with this condition have three copies of the 21st chromosome.

    Continue reading below...

    What Causes Down Syndrome?

    Normally, each cell in the human body contains 23 pairs of chromosomes, which contain the genetic material that determines all our inherited characteristics. We receive half of each chromosome pair from our mother and the other half from our father. Individuals with the most common form of Down syndrome, trisomy 21, have an extra 21st chromosome.

    No one knows exactly why this chromosomal error occurs, but it does appear to be related to the age of the mother.

    At age 25, a woman has a one in 1,250 risk for having a child with Down syndrome.

    The risk increases to one in 952 at age 30, to one in 378 at age 35, to one in 106 at age 40 and one in 35 at age 45.

    However, 80% of children born with Down syndrome are born to mothers under the age of 35. This is because most babies, in general, are born to younger women.

    Be sure to check with your doctor if you are pregnant or plan to become pregnant if you have a family history of Down syndrome.

    WebMD Medical Reference


  • Jonah
    Lv 7
    6 years ago

    Eggs undergo meiosis- they split into one egg and three polar bodies- and that process begins before the mother is even born and continues for each egg until the point that she ovulates with them. Older eggs have been in the process of being made for much longer times and errors are more common that way.

    Sperm, in contrast, is made entirely in the few days before it is ejaculated.

    There is also a theory that older women are less likely to miscarry fetuses with trisomies, as compared to younger women with fetuses that have trisomies.

  • 6 years ago

    Besides age which is a huge factor, genetics, any stress the mother has, and environment are key causes.

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