New Prenatal Screening Tools Offer Information, Anxiety

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If you were pregnant, how much would you want to know ahead of time about what might be wrong with the baby you’re carrying? And how much testing would you do to get those answers?

If you ask a dozen pregnant women that question, you’ll probably get a dozen different answers—but it’s a question that every woman will face at some point in the course of her pregnancy. Prenatal testing has improved to the point where first-trimester screening now offers the opportunity to predict, with more accuracy than ever, which babies are affected by chromosomal and other abnormalities.

The most recent advance in prenatal testing is known as the “ultra screen,” or sometimes simply “first-trimester screening.” In 2005, the American College of Obstetricians and Gynecologists recommended that all pregnant women, regardless of age, be offered this test. That’s a major shift from past policy, in which such tests were usually only recommended for women at increased risk of problems, such as those over 35 or with a family history of chromosomal abnormalities.

The ultra screen involves a combination of two tests, done at around 11 weeks to 12 weeks of pregnancy: an ultrasound that analyzes the thickness of the skin on the back of the baby’s neck (known as nuchal translucency), and a blood test that measures the level of a protein and a hormone in the mother’s blood. When analyzed together, these three measures give doctors and their patients a “one in X” risk for certain conditions, such as trisomy 21 (Down syndrome) and trisomy 13 and 18, two other less common (and more severe) abnormalities.

But although the ultra screen is the most accurate noninvasive testing method available so far for such abnormalities, it’s still a “screening test”—especially so early in pregnancy. In other words, it’s not definitive. And the result isn’t a simple yes or no answer.

Depending on the findings of the three parts of the ultra screen, a woman might be told that there is a one in 5,000 risk that her baby has Down syndrome (or one of the other conditions), or a one in 10 risk, or just about any other set of odds you can imagine. So, for example, a woman may be told that she has a one in 100 chance of having a baby with trisomy 21 (or 13 or 18). That’s a 99 percent chance that she doesn’t—but with this test, it’s still considered an elevated risk.

That’s when the woman and her family have to decide what to do next, particularly if the test indicates that there is an elevated risk of an abnormality. Do they proceed with more invasive testing that can offer more definitive answers, but also carries with it a small but not nonexistent risk of miscarriage? Do they wait for a “level II ultrasound,” available at around 20 weeks of pregnancy, which can answer a lot more questions but still may not be definitive about chromosomal abnormalities? Or simply continue with the pregnancy as they otherwise would have and wait to see what happens when the baby is born?

Everyone’s answer to this question is different, and a number that worries one family may not seem all that high to another. Some people may say that they wouldn’t end the pregnancy regardless, so why proceed with invasive testing? Others say they might indeed choose not to continue the pregnancy, so they want to know everything they can as soon as possible. Still others would not terminate, but feel that it’s important to know if anything is wrong ahead of time, in order to research the baby’s condition and make plans for care.

Here’s what one family—mine—decided to do.

I was 40 years old when I became pregnant for the first time. Right away, that put me at a higher risk for abnormalities. Indeed, when I walked into the midwife’s office to take the ultra screen test, I started out with a one in 73 risk of having a baby with a chromosomal abnormality—whereas a 30-year-old woman would have a risk that was more like one in 400.

At first, everything looked reassuring. The highly experienced ultrasonographer measured the baby’s nuchal thickness at 1.5 mm, which is right where it was expected to be for my stage of pregnancy. She also found something else: the baby’s nasal bone. When the nasal bone is missing at 12 weeks of pregnancy, the odds of Down syndrome are increased, although this finding is still new enough (and difficult enough to assess in centers without enough experience) that it isn’t factored into the ultimate “risk profile” that the ultra screen generates. Still, my husband and I were reassured—so much so that I nearly forgot about the results of the blood tests still to come.

A few days later, the call came, and it nearly knocked the breath out of me. Although my ultrasound had been excellent, the levels of one of the two markers in the blood—one known as beta hCG—were unusually high. That could be for any number of reasons, most of them unknown, but one possible reason was that the baby had Down syndrome. My new risk profile: one in 43. In other words, there was about a 3 percent chance that the baby had Down syndrome, and about a 97 percent chance that he or she didn’t. Fortunately, the test pretty much ruled out the much more severe trisomy 13 and 18, but nevertheless, my risk of having a baby with a serious problem was now even greater than my age would indicate. What should we do next?

We had two options: hurry to get an appointment for chorionic villus sampling (CVS), one of the two invasive tests that can more or less definitively tell you whether or not there is a chromosomal abnormality, or wait a few weeks and have an amniocentesis (the other such test). CVS, which analyzes tiny threadlike structures in the placenta called chorionic villi, must be done by the 13th week of pregnancy; amniocentesis, which analyzes cells shed by the baby into the amniotic fluid, can’t be done until about 15.5 weeks.

For me, the third option—wait and see what happens when the baby is born—wasn’t an option at all. I knew the stress of thinking something might be wrong, but not knowing for sure, would make the next 28 weeks unbearable. My husband and I weren’t sure how we’d proceed if a problem were definitively diagnosed, but we knew we had to know.

We decided that I’d undergo CVS testing because it could be done right away. CVS carries a small risk of miscarriage—around one in 200—but I would be having the test done at one of the top centers in the country, with an expert in the procedure, so I felt reassured. After an anxious weekend spent waiting for the test’s preliminary results, we got the best possible news—everything was fine. Our baby was healthy, and there were no chromosomal abnormalities.

During this very stressful time, I confided in a couple of girlfriends and found out that they, too, had had worrisome test results—for both, it was a “bright spot” on the heart found during an ultrasound. They decided not to undergo further testing, but spent the last months of their pregnancies worried about what might be wrong (nothing was).

After we received our reassuring test results, my husband said, “It’s so great to be sure that everything’s OK, but I wonder if it was worth all the worry we went through?”

That’s the question everyone has to ask themselves when they consider screening tests during pregnancy—because “false positives” happen more often than you might think. For me, knowing that I can (mostly) relax for the next 26 weeks, in the knowledge of a healthy baby, was worth the roller coaster of how we got that knowledge. For someone else, it might not be. As with so much about pregnancy, childbirth and parenting, only you can know what’s right for you. Listen to your doctor and other health professionals, read the literature—and trust your instincts.

About the Author

Gina Shaw is the medical writer for The Washington Diplomat.

Last Edited on November 29, 1999