How frequently does Down Syndrome occur?

Down Syndrome (formerly called mongolism), named after Dr. Langdon Down, who described these children in 1866, occurs in one out of seven hundred births. The chance of having a Down Syndrome baby increases with the age of the mother.

• Women under age 23—1 in 2,000 births
• Women at age 30—1 in 1,300 births
• Women at age 35—1 in 400 births
• Women at age 40—1 in 90 births
• Women at age 45—1 in 32 births
• Women at age 50—1 in 8 births

Depending on how they are presented, these figures can be scary. If a doctor says to a mother, "At age thirty-five you have five times the chance of having a Down Syndrome baby than you did at age twenty," that would scare many senior mothers from conceiving. Here's how I present the risk factors to my patients who ask. At age twenty you had a 99.95 percent chance of not delivering a baby with Down syndrome; at age thirty-five your chances of not delivering a baby with Down Syndrome are 99.75 percent. Doesn't that figure sound more reassuring? This is why, in my opinion, the "thirty-five-year-old scare" is too young, forty-five perhaps? Even at age forty-five you have a 97 percent chance of delivering a baby without Down Syndrome. So, for mothers of later childbearing age, these figures are looking up.

Because of these risk factors, we believe that it is unwarranted to scare a thirty-five-year-old mother into prenatal diagnostic tests (either amniocentesis or chorionic villi sampling). Weigh these facts: At age thirty-five your statistical chance of delivering a Down Syndrome baby is 0.25 percent. However, the risk of damage to a normal preborn baby during these tests may be around 1 percent. At present, the AFP (alpha fetal protein) test is inaccurate for the prenatal diagnosis of Down Syndrome and is a source of much needless worry to pregnant parents. Whether or not you have a prenatal diagnostic testing is an individual judgment call between you and your doctor. But remember, your doctor is legally obligated to offer these tests to any mother thirty-five years of age or older.