Genetic blood tests backed by ob-gyns for at-risk women: study

New, non-invasive tests for chromosomal disorders such as Down syndrome are effective for at-risk mothers-to-be, though there is still not enough evidence to recommend them for all women, US doctors said. The screening tests, which find small amounts of DNA from the fetus in the blood of pregnant women, can help diagnose a few genetic disorders starting late in the first trimester.
"This test is a great test in high-risk women, but it tests for very limited numbers of disorders," said Nancy Rose, chair of the American College of Obstetricians and Gynaecologists (ACOG) Committee on Genetics and a reproductive genetics researcher at Intermountain Healthcare in Salt Lake City. "This is a very exiting time for this kind of technology. We believe it will soon be more expansive and cover more disorders." Women at higher risk include those who are 35 and older, have a family history of genetic disorders or have abnormalities spotted on their ultrasounds.
Babies with Down syndrome, also known as trisomy 21, have three copies of their 21st chromosome instead of two and develop more slowly than other children, both physically and mentally. According to the Centres for Disease Control and Prevention, close to 12 out of every 10,000 babies born in the United States in 1999 through 2003 had Down syndrome. In a committee statement that appeared in Obstetrics & Gynaecology, the ACOG said there is not enough evidence to recommend the non-invasive tests for all women, but they seem to be effective for the at-risk mothers-to-be.
The tests have been available in the United States for about a year, and have caught on quickly for that higher-risk group. Ob-gyns say the blood tests can pick up about 98 percent of Down syndrome cases with a false positive rate of 0.5 percent, meaning one in 200 babies without Down syndrome will mistakenly get a positive result. For those who screen positive, ACOG recommends referred to a genetic counsellor as well as more invasive follow-up testing, such as with amniocentesis. One of the main advantages of the blood tests is that they often all but rule out Down syndrome and make more invasive testing unnecessary, said Diana Bianchi, head of the Mother Infant Research Institute at Tufts Medical Center in Boston. "The invasive procedures have some very small, but real, risks of miscarriage," added Bianchi, who is also on the clinical advisory board of Verinata Health, which offers a version of the DNA test.