Why 80% of babies with Down Syndrome are born to women below age 35

Stumbling upon the post at Womb Within had me reading about Sarah Palin, Down Syndrome and the rumor that the baby is not hers. But this post is not about the Alaskan governor or her family, it’s about Down Syndrome and maternal age.

It is true that a high percentage of children with Down syndrome are born to women younger than 35 years old (80%, says NDSS) fueling the connection that Palin’s 17-year old could likely be the mother to a baby with downs.

Maybe she is, maybe she isn’t. But let’s not get the wrong idea that being young makes one more likely to give birth to a baby with downs.

More women under the age of 35 are giving birth to Down Syndrome babies because prenatal genetic test for this age group is not mandatory. Hence, the mother would not know before birth (or later into the pregnancy) that the baby has Down Syndrome. Again, it doesn’t mean that younger women are at higher risk for carrying babies with downs. On the contrary, the incidence of down Syndrome increases with maternal age. Women age 35 have a 1/365 risk of carrying a fetus with down syndrome; by age 40 the chance increases to 1 in 109.

However, the number of children with Down Syndrome born to women over the age of 35 has substantially decreased in the last decade. Credit this to vast improvements in prenatal screening for genetic disorders, and the increased choice of women to terminate a pregnancy. This means, lesser number of women are continuing with the pregnancy once they learn that the fetus maybe at risk for the chromosomal disorder.

There is also something to be said about prenatal testing for genetic abnormalities. I’ll tell you about that, and my personal story, in a later post.