Tests look for Down syndrome

Pregnant women have a range of prenatal tests to predict whether they are carrying babies with Down syndrome.

One of the most common offered during the first three months combines a fetal ultrasound, which checks for certain physical characteristics of Down syndrome, with a blood test, which looks for two markers associated with the condition. The screening, which is usually done between the 11th and 14th weeks, accurately predicts about 80 percent of cases of Down syndrome and has a false-positive rate of about 5 percent.

Diagnostic tests that analyze cells from the fetus or placenta are far more accurate. The most common is amniocentesis, in which a small amount of amniotic fluid is removed using a needle inserted in the abdomen. Fetal cells are then analyzed. The test detects virtually all cases of Down syndrome and is usually done between the 16th and 20th weeks of pregnancy.

Some studies have found that as many as 90 percent of couples who get a positive result for Down syndrome end the pregnancy. But local fetal genetics counselors, who discuss chromosome defects with expectant couples, said rates vary across the country. Each couple must decide for themselves what is best for their family, said Dr. Julie Moldenhauer, director of reproductive genetics for UNC Hospitals in Chapel Hill.

Kristin Paulyson Nunez, a senior genetic counselor for the Duke University Health System, said many patients she sees continue their pregnancies. If the family does not want to keep the baby, terminating a pregnancy is not the only option when a chromosome defect is diagnosed, she said. Many families are willing adopt children with Down syndrome, she said.