Amniocentesis: Necessary Information or Unnecessary Risk?

Amniocentesis carries a small risk of miscarriage

Gloved hand pointing needle at pregnant woman's stomach
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An amniocentesis is a type of prenatal test that involves inserting a needle through the mother's abdomen to collect a sample of amniotic fluid, and subsequently testing the amniotic fluid to examine the baby's chromosomes. However, amniocentesis can be controversial for two reasons: the test carries a small risk of causing a miscarriage, and the results of the test can also lead to people deciding to terminate their pregnancies.

Thus, some pregnant women fear the test, others decry its use, and still others just aren't sure what all the fuss is about.

What We Know About Amniocentesis

Because they have an increased risk of having a baby with a chromosome disorder, moms over 35 may be offered an amniocentesis or CVS as a routine test. But most other moms are not automatically offered an amniocentesis unless their babies are determined to have a high risk of chromosome disorders. An example would be if the triple or quad screen blood test showed elevated odds of a particular condition.

What's All the Fuss About Amniocentesis?

So if amniocentesis is just a test for chromosome disorders, why are people so concerned about it, one might wonder?

Probably the biggest reason people are concerned about amniocentesis is the small added risk of miscarriage -- and the fact that a range of numbers are used to estimate this risk. Reliable research shows that the risk of an amniocentesis inducing a miscarriage is somewhere around 1 in 400 using modern methods, but some sources still use the older, scarier estimates of a 1 in 200 or even a 1 in 100 risk of miscarriage.

And naturally, some people feel that any added risk -- no matter how small -- is too high.

The other reason why people may be passionately against amniocentesis is because some parents decide to terminate their pregnancies when they learn that the baby has a chromosome disorder. The most common disorder people think of when discussing amniocentesis is Down syndrome, a condition that causes developmental and cognitive impairments.

Some people are morally opposed to termination of babies with Down syndrome, especially because the condition doesn't usually cause life-threatening health problems, and thus people's moral judgments on termination may extend to the amniocentesis test because the test can be a catalyst for people deciding to terminate their pregnancies.

Pros of Amniocentesis

Reasons to have an amniocentesis are many, but the biggest is probably that the test gives you a reasonably conclusive answer as to whether your baby has a serious chromosome disorder. With a 99.4% accuracy rate, the odds are low that your amniocentesis will give you a false positive or negative for a chromosome disorder.

For parents who would choose to terminate pregnancies with chromosome disorders, the accuracy of amniocentesis is a strong pro in favor of having the test.

In addition, despite the common association with Down syndrome screening, an amniocentesis can also confirm or rule out several disorders with a worse prognosis than Down syndrome. It is possible that parents who would not choose to terminate a baby with Down syndrome would consider termination if an amniocentesis revealed a condition with high odds of causing death in early infancy, such as Edwards syndrome or triploidy. In such cases, an amniocentesis can be a reliable way to distinguish which chromosome disorder the baby actually has in the event that a screening test or ultrasound shows nonspecific cause for concern over chromosome disorders.

Finally, regardless of people's feelings on termination, an amniocentesis can help parents and doctors to prepare themselves to deal with a baby's needs at birth. Even parents who would not terminate a pregnancy may prefer to have advance knowledge of the baby's diagnosis so they can research the condition and know what to expect at birth.

Cons of Amniocentesis

The main argument against amniocentesis is the small added risk of miscarriage. There is a lot of conflicted reporting over the actual numbers, but even the accepted estimate of 1 in 400 might be too scary for some moms -- especially those with a history of miscarriage or infertility.

Even moms who receive triple and quad screen results showing a higher odds of chromosome disorders may opt against amniocentesis for this reason.

Because of religious or philosophical beliefs, some moms may feel they would not consider terminating a pregnancy for any reason -- even if the baby had a fatal congenital disorder. With termination being out of the question, these moms may decide that there is no benefit to having an amniocentesis since it would carry a small risk and would not change the outcome.

Where Amniocentesis Stands

It is possible that future research may make the whole debate about amniocentesis irrelevant. Researchers are actively at work creating less invasive tests to screen for chromosome disorders in developing babies, such as by isolating the baby's genetic material from samples of the mother's blood. Time will tell what comes of those efforts, but for now, amniocentesis is what's available.

Using the correct numbers for the risk of miscarrying after an amniocentesis, the natural conclusion would seem to be that moms whose risk of having a baby with a chromosome disorder is less than 1 in 400 should not have an amniocentesis (since the odds of the test causing a miscarriage would be higher).

Moms whose risk of having a baby with a chromosome disorder is higher than 1 in 400, whether due to age or triple/quad screen results, should have the option of having the test done. As with most questions, moms should work with their doctors to make decisions that best fit their philosophical beliefs and medical circumstances.

Sources:

Amniocentesis. American Pregnancy Association. Accessed: Apr. 21, 2009. http://www.americanpregnancy.org/prenataltesting/amniocentesis.html.

Should I have an amniocentesis? CIGNA. Accessed: Apr. 21, 2009. http://www.cigna.com/healthinfo/aa103080.html.

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