New, non-invasive tests for chromosomal disorders should be reserved for pregnant women with a higher-than-average risk of having a baby with Down syndrome, doctors said this week. 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.
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. "This test is a great test in high-risk women, but it tests for very limited numbers of disorders," said Dr. Nancy Rose, chair of the American College of Obstetricians and Gynecologists (ACOG) Committee on Genetics and a reproductive genetics researcher at Intermountain Healthcare in Salt Lake City, Utah. "This is a very exciting time for this kind of technology," she added. "We believe it will soon be more expansive and cover more disorders."
Babies with Down syndrome, also known as trisomy 21, have three copies of their 21st chromosome instead of two and develop slower than other kids, both physically and mentally. According to the Centers for Disease Control and Prevention, close to 12 out of every 10,000 babies born in the U.S. in 1999 through 2003 had Down syndrome. Other genetic disorders that can be spotted on the blood tests occur when there's an extra copy of the 13th or 18th chromosome.
In its new committee statement, ACOG says there is not enough evidence to recommend the non-invasive tests for all women, but they seem to be effective for at-risk mothers-to-be. The tests have been available in the U.S. 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 all women who screen positive for Down syndrome or trisomy 13 or 18, ACOG recommends referral to a genetic counselor as well as more invasive follow-up testing, such as with amniocentesis. "It's a screening test - it doesn't tell you for certain that you have a baby with one of these disorders," Rose told Reuters Health. Her committee's statement is published in the journal Obstetrics & Gynecology.
One of the main advantages of the blood tests is they often all but rule out Down syndrome and make more invasive testing unnecessary, according to Dr. 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," said Bianchi, who is also on the clinical advisory board of Verinata Health, which offers a version of the DNA test.
Both Bianchi and Glenn Palomaki, who has studied the technique at Women & Infants Hospital and Alpert Medical School of Brown University in Providence, Rhode Island, told Reuters Health they agreed with the new statement. "Although this is a really good test, it still isn't perfect," said Palomaki, who, like Bianchi, wasn't on the ACOG committee. He said with more research - and once the price of the tests goes down - they may be offered to all pregnant women. Palomaki also said companies are developing more uses for them, such as to identify gender and other genetic disorders like Turner syndrome. Running the blood tests now costs $1,200 to $2,700 each, according to Bianchi, but the majority of that is typically covered by insurance.
Source: Chicago Tribune