Pregnancy blood test can identify Down's syndrome
The tests are already proving controversial, with opponents of abortion concerned that more women will decide to terminate their pregnancy. "We oppose testing for the purpose of killing unborn children who are found to have disabilities," says Jessica Rodgers, spokeswoman for the National Right to Life Committee.
Brian Skotko, a Down's syndrome researcher at Harvard Children's Hospital in Cambridge, Massachusetts, says this isn't an unreasonable concern. The new tests will see prenatal diagnoses skyrocket, he says. "Unless the healthcare community ensures that these women receive accurate information about Down's syndrome, I think that a reasonable prediction is that fewer babies with the syndrome will be born."
Down's syndrome, caused by an extra copy of chromosome 21, is generally detected by amniocentesis, which involves inserting a needle into a pregnant woman's belly to sample cells from the fluid bathing her fetus. It carries a 1 per cent risk of miscarriage and is usually performed between 15 and 20 weeks into pregnancy - which in some US states is right up against the legal time limit for abortion. Chorionic villus sampling, which samples tissue from the placenta, can be performed earlier, but has an even higher risk.
The new tests instead detect DNA from fetal cells that have broken down. Some of this DNA crosses the placenta and gets into the mother's bloodstream, and the tests look for an excess of material from fetal chromosome 21.
First out of the gate was Sequenom of San Diego, which launched its long-awaited test for Down's last October. Verinata of Redwood City released its test in March, while Ariosa Diagnostics of San Jose will launch a test this week; both of these can detect extra copies of chromosomes 13 and 18 too, each associated with distinct chromosomal conditions. Later this year, Natera of San Carlos will market a test that can also detect additional copies of the X and Y sex chromosomes.
Not only do the blood tests eliminate the risk of miscarriage, they are also claimed to have lower error rates than conventional tests. At a conference on prenatal genetic testing at Stanford University in California last week, Kenneth Song of Ariosa said that its test turns up false positives in less than 0.1 per cent of cases - compared with 5 per cent from invasive tests. The other companies report similar results.
The new tests can be run from about 10 weeks into pregnancy. In some US states, the extra time this will allow may be crucial as women decide whether to carry a fetus to term. Nine states currently ban abortions after 20 weeks on the grounds that a fetus can feel pain at this age; 11 others are considering such legislation.
Will the extra time lead to a surge in abortions? That fear "gives women too little credit", argues Jaime King of the University of California Hastings College of the Law in San Francisco. She suggests that if women have more time to gather information on raising disabled children they might be more likely to keep the pregnancy.
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- 13:54 07 June 2012 by Sara Reardon
- For similar stories, visit the Genetics Topic Guide
The tests are already proving controversial, with opponents of abortion concerned that more women will decide to terminate their pregnancy. "We oppose testing for the purpose of killing unborn children who are found to have disabilities," says Jessica Rodgers, spokeswoman for the National Right to Life Committee.
Brian Skotko, a Down's syndrome researcher at Harvard Children's Hospital in Cambridge, Massachusetts, says this isn't an unreasonable concern. The new tests will see prenatal diagnoses skyrocket, he says. "Unless the healthcare community ensures that these women receive accurate information about Down's syndrome, I think that a reasonable prediction is that fewer babies with the syndrome will be born."
Down's syndrome, caused by an extra copy of chromosome 21, is generally detected by amniocentesis, which involves inserting a needle into a pregnant woman's belly to sample cells from the fluid bathing her fetus. It carries a 1 per cent risk of miscarriage and is usually performed between 15 and 20 weeks into pregnancy - which in some US states is right up against the legal time limit for abortion. Chorionic villus sampling, which samples tissue from the placenta, can be performed earlier, but has an even higher risk.
The new tests instead detect DNA from fetal cells that have broken down. Some of this DNA crosses the placenta and gets into the mother's bloodstream, and the tests look for an excess of material from fetal chromosome 21.
First out of the gate was Sequenom of San Diego, which launched its long-awaited test for Down's last October. Verinata of Redwood City released its test in March, while Ariosa Diagnostics of San Jose will launch a test this week; both of these can detect extra copies of chromosomes 13 and 18 too, each associated with distinct chromosomal conditions. Later this year, Natera of San Carlos will market a test that can also detect additional copies of the X and Y sex chromosomes.
Not only do the blood tests eliminate the risk of miscarriage, they are also claimed to have lower error rates than conventional tests. At a conference on prenatal genetic testing at Stanford University in California last week, Kenneth Song of Ariosa said that its test turns up false positives in less than 0.1 per cent of cases - compared with 5 per cent from invasive tests. The other companies report similar results.
The new tests can be run from about 10 weeks into pregnancy. In some US states, the extra time this will allow may be crucial as women decide whether to carry a fetus to term. Nine states currently ban abortions after 20 weeks on the grounds that a fetus can feel pain at this age; 11 others are considering such legislation.
Will the extra time lead to a surge in abortions? That fear "gives women too little credit", argues Jaime King of the University of California Hastings College of the Law in San Francisco. She suggests that if women have more time to gather information on raising disabled children they might be more likely to keep the pregnancy.
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