By Tracey Porpora

New, earlier test for Down syndrome

  |  Advice & News: Kids With Special Needs  

With more women choosing to give birth over age 35, physicians are taking advantage of new testing measures that can identify 85 percent of Down syndrome cases in first trimester screening procedures. While most doctors screen their patients for their risk — which increases with maternal age — of having a baby with a chromosomal abnormality in the second trimester with a Level 2 sonogram, not all have initiated first trimester screening. The new screening tools, which consist of blood tests and a sonogram known as Nuchal Translucency, can alert a woman of her risk of having a Down syndrome baby as soon as 11 weeks into the pregnancy. And unlike other invasive procedures, such as chorionic villus sampling (CVS) or amniocentesis, there are no risks of miscarriage associated with these tests. Although amniocentesis still remains the only 99 percent effective means for diagnosing chromosomal abnormalities, one in 200 pregnancies will result in miscarriage as a result of the test, which is performed around the 18th week of pregnancy by inserting a thin needle through the abdomen into the uterus to withdraw a small amount of amniotic fluid. (CVS is another invasive procedure that has an even higher risk of miscarriage than the amniocentesis, but can be done in the first trimester, and is performed by removing a small sample of the placenta from the uterus through either a catheter or needle). While the National Institutes of Health recommends amniocentesis for all women who will be 35 or older when they give birth, many women in this age group are choosing to forgo the invasive test simply based on their age. Now, many doctors believe the first and second trimester sonograms and blood tests should be used as first-line screening tools for women of all ages to check for chromosomal abnormalities. “This is a second look at a pregnancy, especially if you’re under the age of recommended amniocentesis, to reassure and give you positive information that you could feel comfortable not having an amniocentesis, or you can possibly catch an abnormal baby,” says Dr. Janice Marks, an obstetrician and gynecologist affiliated with Lenox Hill and New York hospitals. The Nuchal Translucency sonogram — completed in the first trimester between 11 and 13 weeks of pregnancy — measures the thickness of the back of the fetus’s neck to see if its measurement is the appropriate size for its age. “Looking at the thickness of the back of the neck at this time can give you a prediction for aneuploidy, which is an abnormal number of chromosomes,” says Dr. Marks. Recent studies have found that the ultrasound administered in conjunction with blood tests that measure pregnancy hormones is able to diagnose 85 percent of babies with Down syndrome and other chromosomal disorders. “We’ve recently learned that we can improve the accuracy for the Nuchal Translucency by combining it with blood tests,” reports Dr. Stephen Chasen, associate professor of OB/GYN at the Weill Medical College of Cornell University. “We use mom’s age as a starting point, and can adjust her risk based on the results of the ultrasound and blood tests.” Meanwhile, the Level 2 sonogram, which is more widely used by doctors across the country than the newer Nuchal Translucency, is performed between 17 and 20 weeks. It looks at the fetus’s anatomy, such as the heart, kidneys and brain, and can determine whether any other fetal abnormalities are present, including spina bifida. At this time, blood tests — such as the triple or quadruple screens, which check for certain hormones, including alpha-fetoprotein, in the bloodstream — can be administered. “These are blood tests that give us risk ratios that say whether you are at higher or lower risk for Down syndrome,” says Dr. Marks. However, one of the reasons some doctors don’t recommend Nuchal Translucency is the risk of “false positives” or contradictory results on first and second trimester screening tests. “These tests can give a positive result, which means you’re at increased risk for Down syndrome, but that doesn’t mean the baby has it, it just means that you’re at a higher risk,” says Dr. Marks. “It can also come back normal, and your baby could have Down syndrome. The false-negative rate [of Nuchal Translucency] is about 15 percent. It’s most important for every patient to understand their risk of having an abnormal pregnancy, and what the false positive and false negative rate is for these tests.” Another reason for doctors’ hesitance toward ordering the Nuchal Translucency test is that if performed incorrectly, the ultrasound can result in a false positive. “The Nuchal Translucency test has been controversial because it is a very difficult test to do right,” says Dr. Chasen, who also is the director of High Risk Obstetrics at New York Presbyterian Hospital’s Cornell Campus. “There are studies that show that some centers have had a very high false positive rate and low detection rate.” For this reason, he recommends questioning perinatologists or radiologists about their experience administering the ultrasound, as well as to make sure they are accredited by the Fetal Medical Foundation to perform the test. While most insurance plans will cover all the screening tests, women should check with their individual companies if they are concerned about coverage.