Down Syndrome Is Most Common In Women Under 35, But Why?

October is Down Syndrome Awareness Month. Whether or not you’re the parent of a child with Down syndrome, understanding more about Down syndrome is critical because Down syndrome is the most common chromosomal condition. I was personally surprised to learn that, according to the CDC, babies born with Down syndrome account for one out of every 691 live births in the United States, a figure that is up from one in 1087 in 1990.  You may already know someone with Down syndrome, but if you don’t, you likely will soon. They may be your child’s classmate, or working at a store you frequent, or a new member of your family.

But with Down syndrome such a common chromosomal condition in the United States, why aren’t more people aware of the facts about Down syndrome and Down syndrome screening, including the fact that most babies with Down syndrome are born to women under 35?

Down Syndrome Screening

SINCE WOMEN UNDER THE AGE OF 35 HAVE FAR HIGHER FERTILITY RATES, THE VAST MAJORITY OF CHILDREN WITH DOWN SYNDROME ARE BORN TO MOTHERS UNDER THE AGE OF 35.

The relationship between maternal age and the likelihood of conceiving a child with Down syndrome is commonly misunderstood. It’s true that individual women over the age of 35 have substantially higher chances of conceiving a child who has Down syndrome. According to the March of Dimes, a 40-year-old woman has a one in 100 chance of having a baby with Down syndrome. This seems like a rather high rate compared to the chance of one in 1,250 at age 25, or one in 1,000 at age 30, or, even, one in 400 at age 35.  However — and here’s where things get a bit unexpected — since women under the age of 35 have far higher fertility rates, the vast majority of children with Down syndrome are born to mothers under the age of 35.

Screening for Down syndrome in early pregnancy is increasingly becoming the norm and should be offered by practitioners to all pregnant women at this stage. Many screening tests are covered by insurance, although not in all instances. Out of pocket costs vary, depending on practitioners and whether or not they subsidize or cap out of pocket costs for recommended tests. I spoke with a number of mothers who are currently pregnant or had babies in the last three months — ranging in age from 24-39 — all of whom were offered early screening, although some of them declined testing. Dr. Nicole Baumer, the Director of the Boston Children’s Hospital Down Syndrome Program, and Dr. Emily Davidson a pediatrician in Boston Children’s Complex Care Service explain, “The American College of Obstetricians and Gynecologists (ACOG) recommends offering prenatal screening for all pregnant women, regardless of risk factors.” Since the ACOG made this recommendation in March of this year, insurance coverage for these screening tests will no doubt increase.

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