Why Are We So Surprised By Major Birth Defects?

Health and medicine explained.
Oct. 19 2011 11:33 AM

A Womb Without a View

Major birth defects come as a surprise for most parents, but they don’t have to.

Newborn baby.
Prenatal screenings including ultrasounds, while not without controversy, are improving

Photo by Photodisc/Thinkstock.

Here’s something to freak out expectant parents: Over 2 percent of all American pregnancies are complicated by serious birth defects, and more than 0.5 percent of all fetuses have either a missing or an extra chromosome—a condition that leads to problems like Down or Edwards syndrome. Birth defects are a leading cause of infant mortality in the country, and most problems occur in pregnancies without any obvious risk factors. (For example, most babies with Down syndrome are born to women under 35 years of age.) There are ways to screen fetuses for birth defects like these, but due to a lack of clear guidance from caregivers or policymakers, parents may not find out about them until it’s too late.

Knowing about problems before birth is important for at least two reasons. First, it allows doctors to treat the condition. Take heart problems, where a major artery may be connected incorrectly or a pumping chamber may be missing. Prenatal detection and immediate treatment at birth can prevent the sudden oxygen deprivation and shock that might occur if doctors were surprised by the defect. Some types of spina bifida can be surgically fixed before birth, preventing future paralysis.

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A second benefit of prenatal screening is that it gives families a chance to decide whether they wish to continue a pregnancy at all. A huge number of women now choose abortion when faced with major birth defects. In Hawaii, which collects comprehensive information on pregnancy outcomes, more than 90 percent of women who learn they have a fetus with Down syndrome choose to terminate their pregnancies. (Other states are likely to have similar proportions.) Roughly one-half of all women whose babies have brain defects or major abdominal defects also elect abortion. To be sure, many families continue their pregnancies, and love and nurture their babies. Such families deserve support from doctors and insurers. But many families choose differently and they also deserve support.

Most of the time, however, expectant parents never realize there might be a problem. Major heart defects go unnoticed until birth an astounding 70 percent of the time. Three-quarters of all babies with missing limbs come as a surprise to both doctors and patients. More than one-half of cases of Down syndrome are overlooked. The list goes on and on.

Why are we missing so many important birth defects during pregnancy? Insurers and advisory groups don’t support the necessary procedures. To diagnose the vast majority of problems—such as those related to the heart, lung, gut, and brain—one must visualize the fetus’s body by ultrasound during the second trimester. But back in 1993, the New England Journal of Medicine reported results from the so-called RADIUS study (that’s “Routine Antenatal Diagnostic Imaging with Ultrasound”). According to its findings, the blanket use of such ultrasounds “clearly indicate” no impact on a baby’s outcome; parents would do just as well by letting their doctors decide whether to do the scans on a case-by-case basis. As a result, several insurance companies, such as Aetna, don’t cover comprehensive fetal scans for routine pregnancies—a policy that affects roughly one-third of American women. The American Congress of Obstetricians and Gynecologists does not recommend the scan for all women, either. (When my wife was pregnant with our first child, our obstetrician actually advised us to make up a family history of birth defects, since our insurer wouldn’t cover the scan in a normal pregnancy.)

Yet the RADIUS study, now almost 20 years old, shouldn’t guide our approach today. First, treatments have gotten better. RADIUS actually showed that screening increased the number of major birth defects identified by a factor of more than 3—but given the therapies for heart defects and other problems that were available back then, this extra information didn't help. Second, the technology for scanning fetuses has vastly improved. At least one-half of the detections of major birth defects in the RADIUS study came too late for women to consider pregnancy termination; if we did the study over using today's technology, it’s very likely that would change. Third, many parents want to know whether their unborn child has a major birth defect, even if there's nothing they can do about it. (As with many screening tests, false positives worry doctors and policymakers. However, even the RADIUS study showed no measurable harms to babies from ultrasound screening.)

At this point, almost every obstetrician in the country who manages high-risk pregnancies thinks ultrasound screenings are a good idea—so long as they they’re done in a high-quality, high-volume center. (A good center is key since the doctors’ and technicians’ skills vary a lot. Just this month, I saw a pregnant patient who’d been assured her baby was fine, yet a week before birth our ultrasound detected clear signs of a major heart defect, missing stomach, and a malformed brain, among other problems.) Among large, developed Western nations, only the United States, the Netherlands, and Spain fail to recommend complete fetal ultrasounds for all pregnant women. (Germany and France, which have the highest detection rates for major defects, recommend a complete scan every trimester.)

Without comprehensive prenatal ultrasound, women are at the mercy of conventional “risk-based” screening, in the form of a blood test that provides information on three (and only three) potential problems: spina bifida, Down syndrome, and Edwards syndrome. By measuring the levels of estriol, alpha-fetoprotein, and several other substances in a pregnant woman, the test assigns a certain probability to each defect. The lab report reads like a Vegas betting line. For example, a woman of a given age might have a baseline 1-in-476 chance of having a baby with Down syndrome before she even takes the test, and then be told that her true risk, determined from her blood sample, is 1 in 51. (In 2007, ACOG added an ultrasound measurement of the fetus’s neck to the standard test, but continued the practice of reporting proportions.)

That’s a problem because many patients find these statistics utterly baffling. In 1999, researchers found that one-half of all patients can’t make sense of them; for example, many think a 1-in-200 risk of a birth defect is more favorable than a 1-in-400. Perhaps as a result, few women with elevated risks choose to have amniocentesis, the follow-up procedure that would give a more definitive result.

Amniocentesis carries its own risks: It causes miscarriages at a rate that falls between 1 in 300 and 1 in 1,600. How should one probability be weighed against another? Many patients aren’t sure. Interestingly, no regulatory authority tracks doctors’ complication rates with amniocentesis, and ACOG does not set a minimum number of procedures for each doctor per year (meaning that your doctor may not do them often enough to stay sharp).

Given all these concerns, what should expectant women do? No test can catch every problem, of course. Here’s the bottom line: Until sophisticated new blood tests or high-quality scans become widely available—for example, one that provides the same information as amniocentesis but without the risks of miscarriage—the best resource to help navigate prenatal testing is a genetic counselor. These professionals, typically on staff at large birth centers, help women make sense of their options for prenatal testing—and remind them that the usual blood tests cover only a few, relatively uncommon problems. (They also may guide couples of certain high-risk populations, like Ashkenazi Jews, to more specialized testing.) For now, women should also consider a comprehensive fetal ultrasound in the second trimester at a high-volume, tertiary-care center. Otherwise, they may be turning a blind eye to their baby’s health.

Darshak Sanghavi, a pediatric cardiologist, is a fellow of the Brookings Institution and Slate’s health care columnist. Follow him on Twitter.

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