You are here
New Test Screens for Genetic Defects Early in Pregnancy
By Leigh Ann Woodruff, February 28, 2012
A simple, early blood test for detecting fetal chromosomal abnormalities will soon be on the market and may be offered by your doctor. The test, developed by a Stanford scientist and offered by the biotechnology company Verinata Health, can detect Down Syndrome (trisomy 21) with 100 percent specificity (no false positives) and sensitivity; Edwards Syndrome (trisomy 18) with 100 percent specificity and 97.2 percent sensitivity, and Patau syndrome (trisomy 13) with 100 percent specificity and 78.6 percent sensitivity, according to a recent clinical trial.
The new test analyzes fetal DNA in a mother who is 10 weeks pregnant. This spares a woman the risk of miscarriage with a more invasive test such as amniocentesis, which is typically performed at 15 to 20 weeks. In addition, a decision to terminate the pregnancy could be made earlier if a genetic defect was detected. Chorionic villus sampling, another genetic test, is performed earlier between the 10th and 12th weeks, but it is also an invasive test.
"The biggest fear that people have is losing a pregnancy from doing the amniocentesis," says Laurence Jacobs, M.D., a fertility doctor with Fertility Centers of Illinois. "And so if you can have a non-invasive blood test that's not going to not hurt the pregnancy in any way, I think it's clearly of benefit."
The new blood test screens for aneuploidy, which means abnormal numbers of chromosomes. If a couple is undergoing IVF, they can screen for aneuploidy prior to even becoming pregnant with a laboratory technique know as preimplantation genetic screening (PGS). With PGS, the embryos are biopsied and some or all of the 23 pairs of chromosomes are tested for abnormalities. "I typically recommend PGS for women who are in their mid 30s or older, those who have failed IVF several times, couples that have had multiple miscarriages and couples who have severe male factor," Dr. Jacobs says.
Obtaining more information earlier about genetic defects is good for all couples who are planning to have children. While the new blood test and PGS test for aneuploidy, they do not test for single gene defects that cause genetic disease such as cystic fibrosis or Tay Sachs disease. "On each chromosome, there are thousands of genes, and there can be abnormalities in the genes vs. having an extra chromosome such as in Down Syndrome," Dr. Jacobs explains. "There are two different types of genetic problems, one that leads to certain types of abnormalities, and the other leads to certain diseases."
Dr. Jacobs offers all of his patients genetic screening with the Counsyl genetic test. "I offer it to every single couple," he says. "It looks for more than 100 different diseases." If the woman test positive as a carrier for genetic disease, then the male partner is tested for the same condition. "And if they both happen to be positive, then in order to prevent them from having children with those serious problems, that's when you do IVF and preimplantation genetic diagnosis (PGD) because you can test every single embryo for that particular abnormality before you put them into the woman's uterus."
The new Verinata blood test gives doctors just one more weapon in the arsenal of genetic testing. It's can be difficult to screen for every eventuality before becoming pregnant. For example, while PGS screens for chromosomal abnormalities, if you only have PGD, it does not. "With PGD, you can select the embryos that do not have a specific genetic defect, but they may have chromosomal abnormalities," Dr. jacobs says. "The blood test can give you any bad news earlier."
The new blood test's effectiveness was reported in the findings of a Verinata-sponsored clinical trial, which was published in the journal Obstetrics and Gynecology. It accurately detected all 89 cases of Down syndrome in 532 maternal blood samples, 35 of 36 cases of Edwards syndrome and 11 of 14 cases of Patau syndrome.