THURSDAY, Nov. 15, 2001 (HealthDayNews) -- Detecting Down syndrome early in pregnancy could be as plain as the nose on the baby's face.
British scientists say failure to detect a nose bone on ultrasound tests performed at 11 to 14 weeks of gestation is an almost sure sign that the fetus suffers from Down syndrome, a grave genetic disease that prompts many parents to terminate pregnancies. Combined with other important risk factors for the disorder, such as a mother's advancing age, the test is even more accurate at catching affected fetuses, the researchers say.
Lead study author Dr. Kypros Nicolaides, a fetal medicine specialist at King's College, in London, says no other tests available to doctors approach the face picture's ability to detect Down syndrome.
"The bone is white, whereas absence of bone produces a blackness," Nicolaides says. "In a place where you should be seeing a whiteness you are seeing a blackness." New, unpublished results show the combination of nasal bone screening with several other Down syndrome tests can identify the disorder in more than 98 percent of babies, Nicolaides says.
The findings appear in the Nov. 17 issue of The Lancet.
Down syndrome, also known as trisomy 21, is a chromosomal disorder occurring in roughly one in every 800 live births in the United States. The condition produces varying degrees of mental retardation and a range of physical deformities, including a small nose and thick neck, which are detectable more or less in early pregnancy.
Down syndrome can be diagnosed by a procedure called amniocentesis that samples fetal cells in the uterus. However, since amniocentesis can lead to miscarriage, doctors are cautious about ordering the test. Anything to improve the odds of diagnosing the disorder, while minimizing the likelihood of miscarriage, would be welcome, experts say.
Doctors now have four proven screening tools for Down syndrome, each of which is mistakenly positive as much as 5 percent of the time. The first is maternal age, since women over 35 have about a 30 percent risk of carrying babies with Down syndrome. Maternal age and a positive result on a blood test for proteins shed by the placenta identifies 60 percent to 70 percent of affected pregnancies.
The third test uses ultrasound in the first trimester of pregnancy to measure an area on the fetus's neck called the nuchal fold, which is too bulky in Down syndrome babies. When a woman over 35 has a fetus with abnormal nuchal thickness, the risk of Down syndrome is 75 percent. And when the scan, the blood test and maternal age all point to high risk, the odds of Down syndrome are 85 percent.
In the new study, Nicolaides and his colleagues wanted to learn if telltale facial deformities of Down syndrome were apparent early in pregnancy. They used ultrasound scans to look for the nasal bone of 701 fetuses, all of whom were at risk of chromosome anomalies thanks to their mother's age and an abnormally thick nuchal fold.
Only three (or 0.5 percent) of 603 fetuses had abnormal profiles among 601 infants who turned out to have healthy chromosomes, the researchers say. But 43 of the 59 (73 percent) later diagnosed with Down syndrome were missing nose bones in the ultrasound pictures.
That suggests fetuses with no nasal bone on an early ultrasound are about 150 times more likely to have Down syndrome than those with normal profiles, the researchers say. The rate of abnormal nasal profiles also was significantly elevated for fetuses who had other genetic disorders, the researchers say.
"The whole pattern is compatible with delayed maturation," including delayed formation of nasal bone. "That is why the 11-14 week bracket is an important one," Nicolaides says.
Nicolaides's team now is gathering 20,000 women for a trial to see if they can detect Down syndrome in pregnancies that haven't initially been screened for the disorder. The results of that study should be available sometime next year, he says.
Dr. James Goldberg, co-director of the prenatal diagnosis center at the California Pacific Medical Center in San Francisco, predicts the nose bone test "is going to be a very powerful marker" for Down syndrome. While it might take some time to verify the English results and to train doctors to pay attention to fetal nose structure, Goldberg says some physicians in America already are looking for the feature.
"The biggest problem is that a significant percentage of women don't present for prenatal care in the first trimester," Goldberg says. A 1998 study, for example, found that a third of women under age 18, and 17 percent of older women didn't receive a prenatal exam in the first three months of pregnancy, he says.
What To Do
The most important thing you can do if you're expecting a baby is to get regular prenatal care.
To find out more about Down syndrome, try the National Down Syndrome Society or the National Association for Down Syndrome.
To learn more about ultrasounds in pregnancy, try the Women's Health Alliance.
