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.

(Continued from Page 1)

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.)

Advertisement

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.

TODAY IN SLATE

Sports Nut

Grandmaster Clash

One of the most amazing feats in chess history just happened, and no one noticed.

The Extraordinary Amicus Brief That Attempts to Explain the Wu-Tang Clan to the Supreme Court Justices

Amazon Is Officially a Gadget Company. Here Are Its Six New Devices.

Do the Celebrities Whose Nude Photos Were Stolen Have a Case Against Apple?

The NFL Explains How It Sees “the Role of the Female”

Future Tense

Amazon Is Now a Gadget Company

Food

How to Order Chinese Food

First, stop thinking of it as “Chinese food.”

Scotland Is Inspiring Secessionists Across America

The Country Where Women Aren’t Allowed to Work Once They’re 36 Weeks’ Pregnant

The XX Factor
Sept. 18 2014 11:40 AM The Country Where Women Aren’t Allowed to Work Once They’re 36 Weeks’ Pregnant
Moneybox
Sept. 17 2014 5:10 PM The Most Awkward Scenario in Which a Man Can Hold a Door for a Woman
  News & Politics
Weigel
Sept. 18 2014 3:19 PM In Defense of Congress Leaving Town Without a New War Vote
  Business
Moneybox
Sept. 18 2014 5:09 PM Three CEOs Step Down in 30 Minutes
  Life
Outward
Sept. 18 2014 4:15 PM Reactions to a Sketch of Chelsea Manning Reveal Transmisogyny
  Double X
The XX Factor
Sept. 18 2014 3:30 PM How Crisis Pregnancy Centers Trick Women
  Slate Plus
Behind the Scenes
Sept. 18 2014 1:23 PM “It’s Not Every Day That You Can Beat the World Champion” An exclusive interview with chess grandmaster Fabiano Caruana.
  Arts
Brow Beat
Sept. 18 2014 4:33 PM The Top 5 Dadsplaining Moments From The Cosby Show
  Technology
Future Tense
Sept. 18 2014 5:43 PM Oracle’s Larry Ellison Steps Down, Will Be Replaced by Hurd’n’Catz
  Health & Science
Science
Sept. 18 2014 3:35 PM Do People Still Die of Rabies? And how do you know if an animal is rabid?
  Sports
Sports Nut
Sept. 18 2014 11:42 AM Grandmaster Clash One of the most amazing feats in chess history just happened, and no one noticed.