Ms. Peterson, 31, the chief of self-advocacy for the National Down Syndrome Society, prefers public speaking and travel. And her test aversion extends to the latest one designed to detect Down in a fetus. "I don't want to think like we're being judged against," Ms. Peterson said. "Not meeting their expectations."
Heralded in the Nov. 10 issue of The New England Journal of Medicine, the new prenatal test provides earlier, more reliable results for all women than the current test, which is routinely offered to only older women who are at higher risk. But for people with Down syndrome and the cluster of other conditions subject to prenatal screening, the new test comes with a certain chill.
Because such tests often lead to abortions, people with conditions from mental disability to cystic fibrosis may find their numbers dwindling. As a result, some fear, their lives may become harder just as they are winning the fight for greater inclusion.
"We're trying to make a place for ourselves in society at a time when science is trying to remove at least some of us," said Andrew Imparato, president of the American Association of People With Disabilities, who suffers from bipolar disorder. "For me, it's very scary."
Some bioethicists envision a dystopia where parents who choose to forgo genetic testing are shunned, or their children are denied insurance. Parents and people with disabilities fear they may simply be more lonely. And less money may be devoted to cures and education.
The Cystic Fibrosis Foundation, for instance, does not endorse prenatal testing, which the American College of Obstetricians and Gynecologists recommends offering during pregnancy.
"If you can terminate pregnancies with a condition, who is going to put research dollars into it?" said Nancy Press, a professor of medical anthropology at Oregon Health and Science University.
Indeed, the $15 million spent on the new test for Down by the National Institute of Child Health and Human Development might have gone instead toward much-needed research on the biochemistry of people living with the condition, said Michael Bérubé, co-director of the disabilities studies program at Pennsylvania State University.
Mr. Bérubé, whose 14-year-old son has Down syndrome, worries that if fewer children are born with the condition, hard-won advances like including them in mainstream schools may lose support. "The more people who think the condition is grounds for termination of a pregnancy, the more likely it will be that you'll wind up with a society that doesn't welcome those people once they're here," he said. "It turns into a vicious cycle."
Anthony Shriver, founder of Best Buddies, a nonprofit organization that helps people with intellectual disabilities form friendships, said smaller numbers will mean even greater social isolation for the people his group serves.
"Loneliness is one of the most significant challenges they face," Mr. Shriver said. "And it would only become more acute as they became a smaller segment of the population."
Beyond the impact on the disabled, disabilities activists say, the implications of prenatal testing for diversity and democracy require more attention than they have so far received.
Lisa Hedley, whose 10-year-old daughter has dwarfism, said the condition is usually not detected prenatally. It is so rare that it has traditionally not been considered worth the expense of the genetic test. Soon, though, pregnant women may be offered a gene-chip technology that can perform hundreds of tests at once for a few hundred dollars.
"It's so complicated," said Ms. Hedley, president of the Children of Difference Foundation. "Would I choose to have my child have a disability? Oh my goodness, no. It's difficult for her. It's difficult for everyone. But difference is what makes the world go round."
Supporters of abortion are especially wary of wading into a discussion over the ethics of prenatal testing, lest they be seen as playing into the opposing side in the fraught national debate over abortion rights. But advocates for people with disabilities are troubled by how much faster the science of prenatal testing is advancing than the public discussion of how it ought to be used.
If no child is ever born again with the fatal childhood disease Tay-Sachs, many might see that as a medical triumph. But what about other conditions, including deafness, which some do not consider to be a disability, and Huntington's Disease, an adult-onset neurological disorder?
Among the difficult choices facing prospective parents in coming years, genetics researchers say, will be the ability to predict the degree of severity in chromosomal abnormalities like Down syndrome, which can cause mild to moderate retardation.
"Where do you draw the line?" said Mark A. Rothstein, director of the Bioethics Institute at the University of Louisville School of Medicine. "On the one hand we have to view this as a positive in terms of preventing disability and illness. But at what point are we engaging in eugenics and not accepting the normal diversity within a population?"
Abortion, Mr. Rothstein and others fear, could become a kind of "poor man's gene therapy," if cost-conscious health insurance companies see it as less expensive than treating a disabled child. Others argue that prenatal testing will be limited to those who can afford it, leaving the poor to grapple with genetic disability and disease.
Of course, as more conditions are diagnosed in utero, many parents may simply decline testing, or use the information to prepare themselves. But studies have shown that women are considerably more likely to terminate their pregnancies if they know of fetal anomalies.
One study of 53,000 women's choices, published in Obstetrics & Gynecology in 2002, found that the termination rate ranged from about 1 percent for conditions that were classified as having no impact on the quality of life, to 50 percent for those considered to have a serious impact.
Women were far more likely to choose abortions for disabilities that have a high probability of affecting cognitive functioning. For conditions that have little or no impact on the quality of life but might require medical or surgical therapy, the abortion rate was 16 percent, but doubled for those likely to cause mental dysfunction.
As for Down syndrome, doctors estimate that about 80 percent of women who get positive test results choose abortion.
Still, some who work with Down syndrome children don't believe the future is that grim. Allen C. Crocker, director of the Down syndrome program at Children's Hospital Boston, believes that number of women who choose to continue their pregnancies will go up in the coming years.
Even as genetic tests appear to have lowered the number of Down syndrome births, he said, social conditions for people with the conditions have improved markedly.
"We're in the midst of a gentle social revolution," said Dr. Crocker, and, he believes, it may just outpace the scientific one.