Newer procedures do not carry the risk of triggering a miscarriage or other complication associated with the more traditional diagnostic methods
By: Jeffrey Gross, M.D.
Historically, 35 has been the age at which amniocentesis and chorionic villus sampling (CVS) have been offered to pregnant women for the detection of Down Syndrome and other chromosomal abnormalities in unborn children. These tests are considered invasive because they do carry some risk of triggering a miscarriage or other complication in the pregnancy.
Statistically, 35 is the age at which the danger of such a complication is just about equal to the risk of having a baby with a chromosomal defect, a risk that increases with the mother’s age at the time of pregnancy. At age 25, a woman has a 1 in 1,250 risk of having a baby with Down Syndrome. By age 40, that risk zooms to 1 in 106.
Now the American College of Obstetricians and Gynecologists (ACOG), in new guidelines published in the January issue of "Obstetrics and Gynecology," is recommending that screening for Down Syndrome and other chromosomal abnormalities be expanded to include pregnant women of all ages, thanks to newer, less invasive screening procedures that have been developed in recent years.
These procedures do not carry the risk of triggering a miscarriage or other complication associated with the more traditional diagnostic methods. CVS, performed at 11 weeks into the pregnancy, can carry as high a rate as 1 in 100 of causing a complication that can result in the loss of the pregnancy. Amniocentesis, usually performed 16 weeks into the pregnancy, can carry a complication rate of 1 in 200.
One of the newer screening methods is called the first trimester screen or nuchal translucency (NT), typically performed 11 to 14 weeks into the pregnancy. It is a combination of a blood test and an ultrasound exam that measures the swelling of the fluid under the skin around the neck of the fetus. Down Syndrome babies characteristically have excessive folds of skin in the back of the neck. This test will pick up 80-90 percent of cases of Down Syndrome.
The quadruple (quad) screen is a four-part blood test that is done between 15 and 20 weeks to detect the presence of abnormal levels of proteins, hormones and biochemical markers. The quad screen represents the latest progression of a blood test that has been offered to pregnant women. It has proven effective in picking up 70-80 percent of Down Syndrome.
It is when these two tests, the quad screen and the nuchal translucency, are put together in an integrated approach that they can provide the most powerful tool to discover Down Syndrome and other chromosomal abnormalities in utero without causing danger to the mother or the fetus.
The ACOG guidelines recommend that women who undergo either of these screening procedures and are found to be at increased risk for having a baby with Down Syndrome should then be offered genetic counseling and the option of amniocentesis or CVS.
The guidelines also discuss a number of factors that should be considered to determine which screening method is optimal which tests are available, how far along the pregnancy is, and whether the mother is carrying more than one fetus. Her personal history is taken into account as is family history, as well.
It should be clear that these newer tests do not screen for all chromosomal abnormalities or types of defects that can occur to the fetus in utero. In addition, the tests may carry a false positive rate as well as a false negative rate.
Patients should check with their insurance companies to find out which of the screening tests are covered. Many insurance companies consider the nuchal translucency screen still investigational so they may not cover the costs. On the other hand, a quad screen is considered standard of care so it is typically covered by insurance.
Ultimately, some combination of the two tests will likely be considered standard of care. University Medical Center at Princeton offers pregnant women the quadruple blood test and the nuchal translucency screening as well as the traditional CVS and amniocentesis. The new ACOG guidelines effectively erase any age distinction when it comes to offering screening for Down Syndrome and other chromosomal abnormalities. That means older women may opt for a screening test like nuchal translucency or a quad screen which predicts risk but is not 100 percent diagnostic. Conversely, younger women may opt for a diagnostic test such as amniocentesis, which is more invasive, risky and expensive, but is also more accurate.
There is no cookie-cutter one-size-fits-all approach. It is difficult to come up with one recommendation because everybody has different values and views about what testing should be used for. But when it comes to their health and the health of their unborn children, women should have all the information they need to make an informed decision. This is why all good prenatal care and screening should be based on an open and continuing conversation with their physician.
For more information about the Maternity Program at University Medical Center at Princeton or to find a physician with Princeton HealthCare System, call (888) 742-7496 or visit www.princetonhcs.org.

