Amniocentesis is less risky now than in past

Email|Print|Single Page| Text size + By Carey Goldberg
Globe Staff / April 7, 2008

When she was pregnant the first time at 33, Jeanine Goodwin agonized and analyzed, wrestling with one of the hardest decisions that modern mothers-to-be can face. Should she get an amniocentesis or shouldn't she?

She wanted to know whether her fetus had Down Syndrome or other chromosomal defects; but the procedure, which involves inserting a needle into the uterus to draw out fluid, also carried a tiny but terrifying risk of miscarriage. "It was always on my mind," said Goodwin, a Back Bay lawyer. "It complicates the whole peace of mind that you're trying to achieve throughout your pregnancy."

Goodwin, now mother to 2-year-old Ryan, is pregnant again, but the decision to take the test came much more easily. She is an amnio veteran, and "this time around, the numbers have gone much more in pregnant women's favor. That's the reason that this time, I didn't even flinch."

For years, the widely accepted odds that an amnio would cause a miscarriage were 1 in 200. But now, though the exact odds remains unclear, the consensus is shifting toward a lower risk - perhaps much lower, thanks to improved techniques.

Last month, the top obstetrics journal, Obstetrics and Gynecology, published an article by Washington University at St. Louis researchers reporting that over 16 years, among more than 50,000 of their patients, amniocentesis appeared to cause a miscarriage in only 1 out of 769 procedures. And in 2006, a similarly large study known by the acronym FASTER estimated the miscarriage risk at just 1 out of 1,600 procedures.

Those numbers remain hotly debated because of methodological issues in the studies. But already, obstetricians and genetic counselors are beginning to change the general risk picture they paint for patients.

Dr. Allan Nadel, director of prenatal diagnostics at Massachusetts General Hospital, tells patients, "The number is less than 1 in 200," he said, "and if they press me, we're telling people 1 in 600, but that's just a guess." The data are deeply flawed, he said, "but those are the only data we have."

The American College of Obstetricians and Gynecologists, or ACOG, put in its latest practice bulletin for amnio providers that the risk was "as low as 1 in 300 to 1 in 500 and perhaps lower," said Dr. James Goldberg, a San Francisco obstetrician who was involved in formulating the bulletin.

"I think most of us who do amniocentesis would agree that the risk has dropped pretty significantly over the last 10 years or so," he said.

The drop is likely due to improvements in ultrasound, which doctors use to guide the needle inside the womb, and ever-more-experienced providers, Goldberg said. Also, the needles used have become skinnier.

It remains to be seen, he said, whether more reassuring risk estimates will translate into more women opting to have amniocentesis. The decision, as any pregnant woman will attest, goes far deeper than a simple weighing of the odds.

"You can crunch numbers all day long intellectually," said Judith Jackson, a certified genetic counselor at South Shore Hospital. "But the decision for many couples includes a larger emotional component and they may focus on what will have more of an impact on their life: Having a baby with a chromosome problem and not knowing at delivery, or losing a pregnancy as a result of the procedure."

The new numbers also come at a time of flux for amniocentesis, which has been used routinely since the 1970s to detect chromosomal problems such as Down Syndrome, mainly in older mothers-to-be, whose risk is highest. When chromosomal defects are picked up, many couples decide to abort.

The long-accepted practice was for doctors to automatically offer amniocentesis to all women over 35 and any others considered at high risk. But age 35 was a largely arbitrary cutoff: It simply marked the point on a graph where the risk of the amnio - 1 in 200 - matched the risk of having a fetus with chromosomal problems - also 1 in 200.

In recent years, advances in early, noninvasive screening for fetal defects - blood tests and ultrasound scans - have led to a drop in amnio use and a shift in thinking: All women should be screened for signs of problems and offered amnios if these screens raise red flags, the new thinking goes. And, ACOG resolved last year, all women should have the option of an amniocentesis, regardless of age.

In practice, Nadel said, insurance generally still pays for amniocentesis only for pregnant women who are over 35, are flagged by a screening test, or deemed at high risk for other reasons. Those are generally the only women who choose to have the procedure.

At the very least, the new amnio risk numbers could be comforting for women who are set on having the procedure, providers say. But the risk is still not zero, and for many women, any risk, however small, is hard to bear.

In the end, said Jackson, perhaps the right approach is simply, "Do the best you can to make the best decision you can, and then go with it and try not to second-guess yourself."

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