The New Prenatal Testing: No Risk of Miscarriage

Photograph of a woman giving blood by Keith Brofsky/Photodisc/Getty Images.

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Amniocentesis, in which a needle is thrust into a woman’s womb in order to test for fetal abnormalities, can be nerve-wracking. Although the risk of miscarriage is small, especially at high-end facilities, the discomfort it evokes in pregnant woman is sometimes primal. “My womb is a sheltered place, a protected place, the one place my baby should be safe and undisturbed. Yet here was this doctor with this thing, this needle, shattering it,” recalls a woman quoted by anthropologist Rayna Rapp in her classic study of amnio in America.

Another option, chorionic villus sampling, can be done earlier in a pregnancy than amnio (between 10 and 12 weeks rather than typically after 15 weeks) but also involves a needle through the abdomen, or a thin tube through the cervix, to remove a small piece of the placenta. And so until now women who wanted definitive information on Down syndrome and other chromosomal abnormalities had no choice but to undergo an invasive procedure.

But that is likely to change. New prenatal tests are on the way that rely on a blood sample taken from the mother’s arm. They should be commercially available within the next few years. In the long run, as the number of conditions they can detect expands, the new tests may shunt the old invasive ones to the side. Why take a big needle to the belly if a little needle in the arm tells you everything you need to know about your fetus? But if that leads to more prenatal testing overall, is it a good thing?

The new tests take advantage of an alluring discovery: From early in pregnancy, a small amount of DNA from the fetus enters the mother’s blood and circulates in her body. This represents a source of genetic material for examination that scientists didn’t know about until relatively recently. The first genetic testing using this DNA is likely to focus on a small group of problems, including Down syndrome. But over time, testing could look for the full range of chromosomal abnormalities detectable with amnio or chorionic villus sampling. All of this may relieve women of one source of prenatal anxiety—though it won’t make getting the results of genetic tests any less fraught.

Amniocentesis dates from the late 19th century, when physicians in Germany first used it to relieve dangerous levels of pressure in the womb by withdrawing excess amniotic fluid. By the mid-20th century, amnio was also viewed as a window into fetal health. Doctors in the United States and elsewhere used it to assess fetal lung development and to determine the gender of fetuses at high risk for hemophilia (the chances of a boy carrying the disease are much greater). They also saw an opportunity to look for Down syndrome, once the chromosomal cause was identified. Rapp explains that advocates began a drive to offer the test to women at a higher-risk for bearing Down syndrome children: In a pivotal wrongful birth case, a woman whose baby turned out to have the disease successfully sued her doctor.

Since at least the 1990s, amnio rates have been falling, from more than 130,000 procedures in 1990 to fewer than 40,000 in 2005, according to the American College of Obstetricians and Gynecologists. (These figures do not include data from a number of states.) That’s partly because more soon-to-be parents are relying on early, non-invasive screening tests. They can begin in the first trimester, and don’t involve anything more invasive than ultrasounds and blood tests. But though they predict fetal risk for selected abnormalities including Down syndrome, they can’t offer certainty.