Should Genetic Tests Be More Widespread?

For women at risk of having babies with birth defects, fetal genetic testing is commonplace. But now a new study suggests all women, regardless of age, could benefit from tests such as amniocentesis.

Currently, doctors generally recommend genetic testing if there is a family history of genetic birth defects, such as cystic fibrosis or Tay-Sachs disease, and for women aged 35 and older because of the increased possibility of genetic abnormalities— like those seen in Down's Syndrome.

Genetic testing is also performed if the woman has an abnormal ultrasound or if she has previously given birth to a child with a birth defect.

But for most healthy pregnant women under 35, genetic testing is not standard.

Now a new study in the British medical journal Lancet is challenging the idea that age should be a factor in fetal genetic testing. The study examined the costs and benefits in a group of 534 pregnant women aged 16 to 47 and concluded the benefit outweighed the cost of the testing.

The authors found no relationship between benefit of testing and the mother's age or risk status. That means genetic testing could be considered both cost-effective and beneficial to all pregnant women, not simply those over 35 or otherwise at risk.

"The decision was made in the 1970s that the cost of testing was offset by benefits only in women over 35," explains study author Miriam Kuppermann, an associate professor of obstetrics, gynecology, and reproductive sciences at University of California-San Francisco.

Decision-makers in the 1970s concluded the financial burden of fetal genetic testing was regained by aborting pregnancies where the baby had chromosomal abnormalities.

But Kuppermann's study factored in the costs of increased testing, including more genetic counseling, more lab tests and increased risk of miscarriage.

"We have more sophisticated ways of measuring costs and benefits now," she adds.

What Kind of Tests Are Performed?

The most common test is an amniocentesis, which involves sampling the amniotic fluid that surrounds the fetus in the uterus.

A sample of amniotic fluid (less than one ounce) is removed through a fine needle inserted into the uterus through the abdomen. The fluid is then sent to a laboratory for analysis. Different tests can be performed on a sample of amniotic fluid, depending on the genetic risk.

Chorionic villus sampling, or CVS, is a second prenatal test that is used to detect birth defects, genetic diseases, and other problems. During the test, a small sample of cells (called chorionic villi) is taken from the placenta where it attaches to the wall of the uterus. These cells have the same genes as the baby and can be sent for analysis.

One benefit of CVS is that it can be done earlier than amniocentesis and results are usually obtained within 10 days. This allows the parents to make decisions earlier in the pregnancy.

So why aren't all fetuses tested now?

Both amniocentesis and CVS have small associated risks for the mother and her baby. For example, the risk that an amniocentesis could cause a miscarriage is between 1 in 200 and 1 in 400. Injury to the baby or mother, infection or early labor are other potential complications, but all are extremely rare.

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