Santorum says prenatal testing leads to abortions. Read Tucker Carlson’s classic essay on prenatal testing and the abortion of Down syndrome babies.

But Lejeune could not stop what he had unwittingly begun. By the summer of 1967, the American Medical Association had passed a resolution endorsing abortion in cases in which "an infant may be born with incapacitating physical deformity or mental deficiency." A year later, the American College of Obstetricians and Gynecologists came out with a similar policy. A number of states, years before Roe v. Wade, followed suit with laws allowing abortion for the purpose of eliminating children with mental defects, including Down Syndrome.

During the 1970s, genetic testing of pregnant women became routine, a practice encouraged by groups like Planned Parenthood. Since it is an invasive procedure that entails extracting amniotic fluid with a needle from around the child, amniocentesis (like its alternative, chorionic villous sampling) carries a significant risk of miscarriage, in some places as high as one in 100. As a result, the test generally has been reserved for use by women over the age of 34, who are more willing to weigh the risk against that of having a child with Down Syndrome. (The incidence of Down Syndrome increases with maternal age, from about one in 2,000 births at age 20 to one in 10 at age 49.) In 1984, however, it was discovered that a non-invasive blood test could be used to calculate the likelihood of bearing a Down Syndrome child. The blood test made it possible to provide screening for Down Syndrome to women of all ages at no risk to the mother. In 1986, the State of California began requiring physicians to offer the tests to pregnant women. The state's health department now funds much of the screening itself, spending $56 million a year to detect prenatal birth defects.

The rest of the country followed California's lead. Between 1988 and 1993, the number of pregnant women who received blood tests for Down Syndrome doubled, to about 2 million. Almost all the tests were covered by private health insurance or Medicaid. Last year, the American College of Obstetricians and Gynecologists officially recommended Down Syndrome screening for all pregnant women. Although there is no cure or prevention for Down Syndrome—indeed, the only real intervention that can be taken after a positive test result is abortion—prenatal screening is now, in effect, mandatory. Few physicians, regardless of their beliefs on the subject, are willing to risk not offering the test, for fear of being slapped with a "wrongful birth" suit if a handicapped child is born. It has happened, repeatedly.

The rapid growth of prenatal testing has had some undeniably positive effects: A woman who knows she will bear a child with a handicap can plan to deliver in a hospital equipped for risky births. And many couples prefer the opportunity to prepare psychologically for the work of raising a disabled child. By far the most profound effect of prenatal testing, however, has been a staggering increase in the number of abortions.

The trend is clear: More testing invariably leads to more—many more—abortions of Down Syndrome children. "Most women who have children with Down Syndrome did not have the amnio," says Lori Atkins of the National Down Syndrome Society, and there is growing evidence to indicate this is true. A study of data from selected states by the Centers for Disease Control found that the rate of Down Syndrome births to mothers 35 or older dropped by about a third between 1983 and 1990. Another study, conducted over a slightly longer period, pegged the decline at 46 percent.

Larry Edmunds, a CDC statistician who is among the country's acknowledged experts on birth-defect trends, cites data from the 1980s suggesting that abortion reduced the number of children with Down Syndrome born to white women over 35 in the metropolitan Atlanta area by about 70 percent. Of the 30 percent in that study who did bear children with Down Syndrome, Edmunds explains, "those were mainly women who didn't have the test."

Lewis Holmes, a professor of pediatrics at Harvard Medical School who works at Massachusetts General Hospital, says that in his experience, of women who learn they are carrying a Down Syndrome child, "90 percent will say they want to terminate. If you have all the technology available and educate the women as to what their choices are, that will happen."

Far fewer than 90 percent of women support abortion, at least in the abstract, so there is some question as to why so many are choosing it when they find they are carrying children with Down Syndrome. A number of studies have attempted to provide an answer. One, conducted by the Canadian Royal Commission on New Reproductive Technologies, found that, because of pressure from hospital staff, one in four pregnant women "felt obliged" to undergo amniocentesis. Of those who tested positive for a birth defect, one in three believed she was "more or less forced" to have an abortion.

Another study, published this summer in the British Medical Journal, describes the case of one pregnant woman whose child had tested positive for birth defects. Following her doctor's orders, she reported to the labor ward of her hospital for what the physician had termed an "induction." It dawned on the woman, who was five months pregnant, that the "induction" was in fact to be an abortion. Horrified, she returned home and later bore the child.

Laurie Cowan, a physician at the state of Delaware's public health department, readily admits that abortion has had a dramatic effect on births of children with Down Syndrome. "We are seeing a real drop in the rate of [Down Syndrome] children who are born. We're not seeing a drop in the rate of children who are conceived," she says. But like many in the medical profession, Cowan is wary of how such information might be used. Abortion, she explains, "has been a right that people have had. So I hope that in no way you'll do anything to try to take away that right. I'm just very concerned about that. I just hope in no way your work will undermine that." Antiabortion forces, she warns, would allow the procedure "only if the mother is raped, only if she's going to die because of this pregnancy. And that's uncomfortable for me because there are certain things that are pretty close to that."