For half a century, women have relied on invasive and risky tests like amniocentesis, which collects DNA from the womb, to learn whether their unborn child had genetic abnormalities. Better tests are finally here: This past year, researchers demonstrated that they could detect Down syndrome using just 10 milliliters of a pregnant woman’s blood.
In 1997 Dennis Lo, a chemical pathologist at the Chinese University of Hong Kong, first suspected that pieces of fetal DNA might enter the mother’s bloodstream. He proved that hunch right with a chromosome test to determine a developing baby’s sex from a sample of maternal blood. Lo next applied the technique to the detection of genetic conditions. In January he announced that in a study of 753 women, he was able to find an extra copy of fetal chromosome 21 (indicative of Down syndrome) in maternal blood as early as 11 weeks into the pregnancy with nearly 100 percent accuracy and no risk to the fetus. Existing genetic tests cannot be performed until the fetus is around 16 weeks old, and they carry a 1 percent chance of miscarriage.
The San Diego–based genetic diagnosis company Sequenom launched the first noninvasive prenatal screening for Down syndrome using Lo’s technique last October. The test is currently available in some 20 cities nationwide. Over the next few years, similar maternal blood tests could detect hundreds of diseases caused by chromosome abnormalities or mutations, including cystic fibrosis, sickle cell anemia, Tay-Sachs disease, and genetic deafness and blindness. “It’s an exciting time,” Lo says. “Soon, we plan to screen for a whole spectrum of diseases.”