Prenatal Testing: Earlier and More Accurate Than Ever

Parents-to-be can now safely determine their baby's gender, father, and certain chromosomal abnormalities during the first trimester.


In just the past few of years, it has become possible for parents to determine the sex and paternity of their fetus during their first trimester with a maternal blood test. And now another blood test is able to detect five chromosomal abnormalities in fetuses as early as 9 weeks. According to the much-anticipated data published last week, it is able to do so with 99.92 percent accuracy.

Now that the ability to safely determine a fetus's gender or paternity so early on is a reality, it's in the process of being refined by companies like Natera, which has had prenatal paternity tests on the market since last August and hopes to have the chromosome test commercially available this year.

The innovations stem from the discovery, in 1997, that a pregnant woman's blood contains trace amounts of her fetus's DNA, which can be extracted and, thanks to the mapping of the human genome, used to predict a wide variety of traits and conditions tied to the baby's genetic makeup. Many such predictions -- like the ones that could lead to "designer babies" -- are, for the moment, theoretical. But, as Jonathan Sheena, Natera's chief technology officer, explains, once a genetic link has been found for something, there's no reason why tests shouldn't be able to detect it.

Sex-selective abortion is the first consequence of such technology to already become a reality, as reflected by the changing gender ratio in China and India. While tests for chromosomal abnormalities aren't intended for the sole purpose of determining gender, the presence of a Y-chromosome is hard to miss when you're looking at DNA -- parents are typically given the opportunity to opt out from receiving this information.

The House of Representatives declined to outlaw sex-selective abortion in the U.S., but a particular fear here may in fact stem from the ability to screen for disease and disability. In a 2004 survey of American opinion surrounding genetic testing from the Genetics and Public Policy Center, the most commonly cited societal implication of concern to the respondents was the potential of discrimination against the disabled. The possibility of a sex-ratio imbalance was much lower down the list.

It may be a slippery slope, but it will be hard to argue that this newest information won't be safely in the green zone. Of the five chromosomal abnormalities detected by the test, two -- trisomy 18, also known as Edwards syndrome, and trisomy 13, also known as Patau syndrome -- have extremely low survival rates. Half of the fetuses with Edwards syndrome that are carried to term do not survive beyond the first week of life. Eighty percent of infants with Patau syndrome don't make it past their first year. Early testing allows parents more time to be prepared for this tragic outcome.

Down syndrome (trisomy 21) and Turner syndrome (monosomy X), on the other hand, are not at all death sentences. Although characterized by a variety of physical and mental challenges, advocacy groups have gone a long way toward helping people understand that these conditions do not prevent people from having long and fulfilling lives. Some have expressed outrage over the Affordable Care Act's requirement of insurers to cover prenatal genetic testing as "preventative care" for women, making the fair, if mostly semantic point that the only way you can "prevent" Down syndrome is through abortion. Concern over bias against babies with Down syndrome is understandable. But since it is by far the most common of chromosomal abnormalities, with the incidence rate rising to 1 in 100 births for mothers who get pregnant at age 40, it's already something that parents are aware of as a potential risk. With that in mind, it's difficult to argue against the pragmatism of granting them access to as much information as possible.

The fifth abnormality, an extra X-chromosome in males, is accompanied physically by what are better described as characteristics than symptoms, and though it also associated with a degree of language impairment, many men go through life not even knowing that they have the condition. Awareness, in this case, will only ensure that children get early intervention where before they may never have been diagnosed. And while a blood test can let parents know, early and accurately, if their baby's DNA contains any of these chromosomal abnormalities, it is unable to tell them the clinical consequences of their genetic makeup -- with the more wide-ranging conditions, there's no way of knowing how a specific child will be affected.

Ethical issues may just be beside the point here, though. Natera doesn't see its test as a potentially abortion-informing agent, because unlike amniocentesis or chorionic villus sampling (CVS), it is unable to give a definitive diagnosis. Instead, it's a way of safely screening for the possibility of these diagnoses so that woman know whether they should undergo the more invasive tests (which could, theoretically, inform abortions). The accuracy of those tests comes with the risk of miscarriage, and the only other option for women before the advent of blood screening was a safe but unreliable hormone test.

"We don't believe that's a choice that women should have to make in the 21st century," said Sheena. Other blood screening tests currently available, he said, have a 5 percent rate of false positives and a 15 percent rates of false negatives. 

Pricing information for this newest test -- which will undoubtedly affect how influential it will be -- hasn't been released yet, but a similar test, MaterniT21, retails at $1,933. According to a representative, most insurers don't claim to cover the test, but  those with health insurance won't pay more than $235 out of pocket for it.

As Conor Friedersdorf wrote last week, a moral calculus comes along with increased access to information. But if this technology becomes widely available and affordable, the most important impact will be making it safer and easier for parents to know exactly what they're dealing with. If anything, it will provide more time for the ethical deliberations that come later.