ST. LOUIS — A new blood test for pregnant women that can reliably detect Down syndrome in a fetus has raised concerns about the ethical implications of making that information safer and easier to obtain.

The test is more accurate than the blood and ultrasound screenings currently used to gauge the chance that a baby will be born with the syndrome. And it’s safer than invasive tests of the amniotic fluid that carry a small risk of miscarriage.

But families and advocates worry that if the blood test becomes widely used, fewer children with Down syndrome will be born. Studies have shown as many as nine out of 10 pregnancies with a Down syndrome diagnosis end in abortion.

The new blood test, MaterniT21 from the California company Sequenom, checks the fetal DNA present in the mother’s blood for the extra copy of the 21st chromosome that causes the most common form of Down syndrome.

It can be administered as early as 10 weeks into the pregnancy with 99 percent accuracy.

So far, the test has been studied in women at higher risk of delivering a baby with Down syndrome — mothers whose initial screenings were abnormal, who have a family history or are older than 35. About 750,000 pregnancies a year fall into that category, the company estimates.

The blood test is expected to further reduce the number of women who undergo amniocentesis to confirm a Down syndrome diagnosis. Most women already decide against the invasive test, which requires the extraction of amniotic fluid from the uterus, in part because of an estimated 1 in 500 chance of miscarriage.

"Women who are not really interested in invasive testing, many of them would want to go for this (new) test," said Dr. Anthony Odibo, who specializes in fetal care at Washington University in St. Louis. "For many of them it’s really for preparation. Especially here in the Midwest, just knowing does not mean you’re going to terminate."

The blood test is available in 20 cities including St. Louis and is expected to cost up to $235 out of pocket for women with insurance. Results can be expected in eight to 10 days. Unlike amniocentesis, the test does not screen for other fetal abnormalities including spina bifida and more rare forms of Down syndrome.

Company executives said they don’t expect the test to have a significant impact on the birth rate for babies with Down syndrome.

"All that this test does is to provide a safer alternative to the information that is already available to a woman" Dr. Mathias Ehrlich, senior director of research and development at Sequenom. "They can take that information with their doctor into consideration, to make appropriate decisions for their family."

About 1 in 691 babies is born with Down syndrome, which is marked by mild to moderate intellectual disabilities, developmental delays and distinctive facial features. Half of the babies also have heart defects that usually require surgery. Children and adults can experience vision, hearing and speech impairments, thyroid problems and respiratory difficulties. People with Down syndrome can expect to live into their 50s, doctors said.

It’s estimated that 400,000 Americans have Down syndrome. Early intervention and therapy has improved their health and opportunities to attend mainstream classrooms, work and live independently, advocates say.

Families of children with Down syndrome said they fear that widespread use of the new test will lead to more abortions, creating a smaller community with fewer resources.

Most families enrolled in the Down Syndrome Center at St. Louis Children’s Hospital did not receive a prenatal diagnosis, said Niki Armstrong, a genetic counselor at the center.

"A big proportion are not interested in prenatal testing because it would not affect pregnancy outcomes" Armstrong said. "I think that’s a very reasonable option."

The results of the test should be accompanied by educational information and referrals to support groups so parents can make informed decisions, said Christy Klaus, family support coordinator for the Down Syndrome Association of Greater St. Louis.

Klaus added that more than 250 U.S. and Canadian families are on a waiting list at the National Down Syndrome Adoption Network.

The grief parents feel after receiving a diagnosis is understandable, said Trey and Darla Lawrence, whose 18-month-old son Dawson has Down syndrome.

The Lawrences, who live in Imperial, Mo., said their initial reaction of fear and panic lasted about a week after they found out fairly early into the pregnancy.

"By the time he was born it was all joy" Darla Lawrence said over lunch at a cafe where Dawson charmed strangers by blowing kisses. "It would be devastating if we didn’t have children like Dawson."

Expectant parents facing a decision about their pregnancy should also hear the personal, and not just clinical side of the story, Lawrence said.

"They’re the lucky ones. I know most people can’t fathom that," she said. "They will have a love and a presence of joy in their house that just can’t be matched by typical people."

In a survey of more than 2,000 parents of children with Down syndrome, 99 percent said they loved their child and 4 percent regretted having the child, according to results published last month in the American Journal of Medical Genetics.

Parents of children with Down syndrome were careful not to depict an overly sunny experience. There are medical, social and educational challenges that require extra time and money.

But people should know there are more similarities than differences among all children, said Linda Kronmiller, education coordinator for the local Down Syndrome Association.

"He’s just like every other human being with a range of emotions," Kronmiller said, speaking of her 14-year-old son Eric. "If you saw him walking through the school, you wouldn’t notice."