Detecting Down Syndrome Risk

Down syndrome is the most common birth defect in this country, affecting about one in 800 newborns.

Now, The Early Show medical correspondent Emily Senay explains, advances in screening are making it possible to detect the birth defects earlier and more accurately than ever before.

Down syndrome is a birth defect caused by an abnormal chromosome. The chance of giving birth to a child with Down syndrome is higher with a family history and increases as a woman ages.

Children with Down syndrome suffer mental retardation and deformities such as a small head and ears, a flat face and short hands.

Senay says for many years, age was the main criteria used to determine risk. Pregnant women aged 35 and over are routinely offered an amniocentesis in the second trimester to find out whether or not the fetus has any birth defects. Since amniocentesis carries a risk of miscarriage, she explains, more accurate screening will hopefully cut down the number of women who get the invasive test.

Over the years researchers have developed better ways to screen for Down syndrome and other birth defects, and those techniques are now allowing for much earlier and more accurate screening.

The latest study from the New England Journal of Medicine shows that for women over 35, a blood test for two indicators of Down syndrome and an ultrasound in the first trimester (at about eleven weeks) detects 85 percent of Down syndrome cases.

Many cases of Down syndrome babies are in women younger than 35. Senay says, the hope is doctors will be able to screen and catch more cases of Down syndrome in younger women.

If the new battery of tests shows a high risk for Down syndrome, there is a new diagnostic test called a CVS test that can diagnose Down syndrome in the first trimester, so you don't have to wait for an amniocentesis. This, Senay says, allows more time to make decisions about the pregnancy if Down syndrome is confirmed.

The new screening is not in general use yet. But it is available in some areas and many believe it's just a matter of time before it is widely used. The early first trimester screenings will likely increase as more professionals are trained to conduct the newer tests.

For now, the current recommendations are still for screening in the second trimester, or about 20 weeks using a different blood test. It is accurate in identifying about 65 to 75 percent of Down syndrome babies.

Senay says the best advice you can get about parental screenings is to talk to your doctor about the pros, cons, options and risk.