By Patricia Reaney

Reuters

LONDON (Nov. 15) - A new ultrasound test for Down syndrome that measures the nose bone of the fetus could reduce the need for more invasive tests and prevent miscarriages, the test's inventor said Friday.

Professor Kypros Nicolaides, who pioneered the technique at the Harris Birthright Center at King's College Hospital in London, said the test, done during a normal 12-week scan, can detect 75 percent of babies with the chromosomal disorder.

"We found that if this bone is visible, the chances of having Down's goes down quite a lot because babies with Down syndrome have a very flat face and small nose," Nicolaides said in an interview.

"With the new test we will improve the detection (of Down syndrome) by two to three times."

In a very high proportion of babies with Down syndrome the nasal bone is not formed or not visible on a scan at this stage of the pregnancy.

The nasal bone scan, together with blood tests and the mother's age can give doctors a good indication if the baby has the disorder and if the mother should have amniocentesis, a more invasive but conclusive test that carries a small risk of miscarriage.

"This new test will help improve dramatically the detection of Down's and at the same time will reduce dramatically the number of unnecessary amniocentesis," Nicolaides said.

Amniocentesis is recommended for women over 35 because the risk of having a baby with Down syndrome increases with age.

But Nicolaides, who also invented a scan which detects Down syndrome by looking at the collection of fluid behind the neck of the fetus, said not all older women need amniocentesis and some younger women do.

"With that approach you are subjecting a lot of women to an unnecessary amniocentesis which carries a risk of miscarriage of one in a hundred, and at the same time we were missing seven out of 10 babies with Down's," he said.

Many babies with Down syndrome are born to younger women because of their higher overall birth rates.

The disorder occurs when a baby inherits three copies of Chromosome 21 instead of two. Children with Down syndrome suffer physical and developmental problems and mild to severe mental disabilities.

Nicolaides said the two physical characteristics of Down syndrome, a thick neck and flat face, can be seen by ultrasound in the third month of pregnancy.

A preliminary analysis of the nasal bone scan on 701 fetuses, reported in The Lancet medical journal, showed the bone was not visible in 73 percent of fetuses with Down syndrome and in 0.5 percent in babies without the disorder.

If further studies are just as conclusive, Nicolaides expects that by the end of next year the nasal bone scan test could be used universally.

"Throughout the world there are a number of unnecessary amniocentesis that lead to the miscarriage of a lot of healthy, normal babies. We will see a major reduction in that," he said.

13:23 11-15-01