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What you should know about prenatal testing Prenatal Care

What you should know about prenatal testing

Before you plunge the needle, here’s what you need to know about the risks and effectiveness of prenatal testing.

In the past year alone, the market has exploded with new noninvasive screening options and technologies that can detect chromosomal abnormalities even before baby is born. Still, many women don’t look into all of the tests that are available—and the risks they might pose—until something is wrong. Get ahead of the game by familiarizing yourself with standard screens, so you’re prepared and knowledgeable should the need for testing arise.

Screen vs. diagnostic
Before we get into specifics, we need to make an important distinction. There are two categories of assessments you can get during pregnancy: diagnostic tests and screens.

Diagnostic tests extract cells from the baby and therefore have a higher percentage of reliability. With very rare exceptions, these diagnostic tests can tell you whether baby has a genetic abnormality. Because they directly involve the baby, there is a level of risk associated—generally, a 1-in-250 chance of causing a miscarriage.

While diagnostic tests look at cells from your baby, screens look at everything but your baby. Because of that, screens can only predict the probability that your baby will have a genetic abnormality. A screen may include a blood test or ultrasound, and it also takes into account your age, medical background and other contributing characteristics. Because they avoid the baby, screens are considered noninvasive and do not pose any risk to the fetus.

First trimester screening
In addition to looking at personal characteristics such as age and family history, doctors can perform two additional tests—a blood draw and an ultrasound—during your first trimester.

The blood test must be performed after week 9 and shortly before week 14. Doctors look at levels of hCG and PAPP-A found in the mother’s blood. An elevated level of hCG and a low level of PAPP-A indicate a higher risk of carrying a baby with Down syndrome. In addition, a very low level of PAPP-A can indicate a higher risk for pre-eclampsia. The potential harm a blood test poses to baby? Zero. The only physical downside is that mom has to have her blood drawn.

After week 11 until shortly before week 14, you can have an ultrasound that looks at the thickness of the skin fold in the back of baby’s neck. Babies with a thicker neck fold (due to the fluid in that area) have a higher incidence of Down syndrome. Kristen Sharp, MD, an OB/GYN at the Meriter DeForest-Windsor Clinic in DeForest, Wisconsin, and Margo Grady, MS, CGC, genetic counselor at Meriter Hospital in Madison, Wisconsin, recommend that women go to a specialized perinatal center for this exam, which will likely require a referral from your care provider. As Grady explains, the test is measuring for a difference of millimeters, so you need to make sure that the ultrasound technician is certified with this particular test. Like the blood test, the ultrasound poses no risk to the baby.

Quad screen
Because some women don’t find out they are expecting until further along in their pregnancies, they miss the opportunity to have the first trimester screen. These women can opt to have the quad screen in the second trimester instead. The plus side of getting this screen versus the first trimester screen is that it also tests for alpha-fetoprotein (AFP), an indicator of spina bifida. The downside is that the results for Down syndrome are less accurate.

DNA diagnostics
A few years ago, a positive result from a first or second trimester screen would take you directly to a diagnostic option. Thanks to advances in technology, however, there are now intermediate noninvasive screens to precede invasive diagnostics. These tests include MaterniT21 PLUS, Panorama, verifi and Harmony. Although all of these tests work a little differently, they have one major similarity: They use your DNA to gain information about your unborn child.

The four screening tests are produced by different labs and use slightly different technology. MaterniT21 PLUS and verifi look at every single letter of fetal DNA, and when they find a sequence, they call it a read. To get an idea of how complex the technology is, consider this: There are about 20 million reads produced from each blood test.

Harmony follows the same basic technology but looks at only certain sequences. Instead of doing 20 million reads, this exam does about 50,000. Harmony is also the only one of the four tests that is designed for women of all ages, even those who are not at risk (that is, younger than 35 years).
Panorama uses slightly different technology and came on the scene after MaterniT21 PLUS. Instead of looking at fragments of DNA, this exam compares the mother’s DNA to the baby’s DNA to check for chromosomal conditions that could affect the baby’s health.

Test takers
Emotions can run high when it comes time to decide which screen options to go with. For Isabella Hank, a mother of one from Madison, Wisconsin, who has her doctorate in molecular science, the updated technology combined with her anxiety over her advanced maternal age pushed her to take MaterniT21 PLUS. Her co-workers had read about the technology involved in MaterniT21 PLUS in science journals just months before she was offered the exam at her doctor’s office. Even though she knew that the results were not 100 percent accurate, she felt she could breathe easier when her tests came back negative and relax for the rest of her pregnancy.

But the screening experience can change dramatically when you receive a positive result. After a healthy first pregnancy, Jackie Roth, a mother of two in Chicago, viewed the first trimester screen as a routine exam during subsequent pregnancies. But when results came back positive, she was caught off guard. “No matter how prepared you are or what conversations you have with your partner about what you would do in that situation, you don’t know what you will do until you are in those shoes,” she says. In her last three pregnancies, Roth has gone through a variety of screens, and she is currently carrying a baby who she knows will have a genetic disorder.

Emotional risk
There is no risk to the baby for a DNA screen, but do not assume there is no risk for the mother. It’s true that the only physical risk involves the discomfort of having blood drawn or the inconvenience of locating a certified perinatal ultrasound specialist, but Roth warns women that there is emotional risk, especially when you receive a positive result. Getting screened can allow you time to prepare for the future—whatever it may look like—and seek genetic counseling as needed. But before you agree to the assessments, you should make sure you’re prepared to process the results.