A study out of Duke University is shaking up the world of prenatal testing. A group of economists found a flaw in the logic of our current prenatal testing recommendations, and wonder whether amniocentesis (amnio) should be performed less frequently as women age, not more frequently.

The recommendation, until 2007, was that all pregnant women over 35 should be offered the option of prenatal testing–amnio or chorionic villus sampling (CVS)–even though both procedures do involve some level of risk for miscarriage. For CVS, which is done earlier in pregnancy, the risk of miscarriage is thought to be about 1-200; for amnio it’s about 1-400 (though many experts will tell you these numbers change depending on the experience of the person performing the procedure).

These tests are offered to older women based on the logic that the risk of miscarriage is about the same, if not lower, than the risk for chromosomal abnormalities such as Down syndrome.

In 2007, the American College of Obstetricians and Gynecologists (ACOG) came out with a new set of guidelines stating that all women, not just those over 35,  should be informed about the risks and benefits of prenatal testing.

Still most doctors and pregnancy guides still advise couples based on the older 35+ guidelines.

The Duke economists looked at all of this and realized that we haven’t been taking into account the fact that women become less likely to conceive as they age, too. If a 40 year-old woman, for example, were to consider an amnio, she should add into her complex analysis of risks and benefits, the odds of being able to get pregnant again were an amnio-induced miscarriage to happen.  “While the benefits to testing rise with age, so do the costs,” they write.

They came up with a new model for calculating the risk of amnios taking into account decreasing fertility. When they looked at the data, they found that amnios should actually go down as women age, rather than up. “…our model implies a falling, rather than rising, rate of amniocentesis as women approach menopause.”

As Ray Fisman wrote in Slate yesterday, where I learned about this interesting new study, “Though the chances of genetic abnormality spiral upward with age, the chances of successfully conceiving a child spiral downward even faster.”

I must say as an older mother myself, I did take all of this into account. Once you start circling 40, the main focus tends to be conception. The anxiety about miscarriage can give the anxiety about chromosomal abnormalities a run for its money. This is also true for women who have used IFV to become pregnant, and/or who have had numerous miscarriages in the past. Or even one miscarriage. But its very true that the culture of prenatal testing concentrates on those high numbers of chromosomal abnormalities.

The authors of the study maintain that this is a very personal choice; they don’t go so far as to  recommend *against* prenatal testing once a women gets to be a certain age.

I think this is important research. Or at least it makes sense to me. I like that the fancy economists are confirming what many older, miscarriage-suffering moms already know: the choice about prenatal testing  is neither based on simple arithmetic nor to be considered without taking decreased fertility into account.

photo: massdistraction/flickr

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