The Science of Sustainability

Pregnancy and Paternity: New Fetal DNA Testing

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Prenatal paternity tests will actually decrease the number of abortions. Image courtesy of Petteri Sulonen from Helsinki, Finland via Wikimedia Commons.

Imagine you are a woman in a committed relationship. The worst happens and you are raped and become pregnant. What are your options?

Until recently, there was no reliable and safe way to determine paternity in the first trimester. This meant that many women chose to terminate their pregnancy without knowing who the child’s father was. Obviously this is not ideal.

If the woman could determine paternity, she could use that information to help in her decision on whether to terminate the pregnancy. Undoubtedly this would lead to fewer abortions as more women choose to carry their partner’s child to term.

The tricky part of a prenatal paternity test is obviously getting a hold of fetal DNA. One method is amniocentesis. In this procedure, a needle is inserted into the amniotic sac and fluid is withdrawn. This fluid contains a lot of fetal DNA but getting it is not only invasive, it is also normally done somewhere between the 15th and 18th week of pregnancy. This is too late for many women.

Other methods take advantage of the fact that there is a bit of fetal DNA floating around in the plasma of mom’s blood. These tests have the advantage that they are noninvasive and can be done much earlier in pregnancy…sometimes as early as 8 weeks. The disadvantage of the early versions of the test was that they weren’t always as accurate as we’d like.

There are anecdotal cases out there of women losing their partner’s child because they thought the child was the result of the rapist and keeping the rapist’s child because they thought the child was their partner’s. This is obviously unacceptable.

Recently a couple of new tests have come on line that appear to be much more accurate. Both use the fetal DNA found in mom’s blood but use novel strategies to improve accuracy.

Scientists at one testing company present results in a recent article in the New England Journal of Medicine to back up their claims of accuracy. They set up an experiment where they had the mother’s, father’s, and an unrelated man’s DNA along with DNA from the mother’s blood plasma. This was a blind experiment in that the scientists did not know which of the two tubes containing the men’s DNA was from the father. They were able to correctly pick the father in 30 out of 30 cases. They claim the odds of this happening by chance are less than one out of a billion. (For those interested, the test is available here.)

What was their secret? Well, as I talk about here, the key difference is that they focus on small bits of DNA that could have only have come from the dad. Any DNA they find in mom’s blood that doesn’t match hers had to come from the fetus. This eliminates any issues of contaminating DNA from mom. If all of this DNA matches a prospective father’s, then he is most likely the dad.

This company has competition from another testing company that is offering another high-powered test using fetal DNA found in mom’s blood. I’ve talked about the science behind this sort of test recently right here at QUEST. There isn’t a New England Journal article that focuses on their prenatal test per se, but they did manage to sequence the entire genome of a fetus so they are probably up to the task!

Even though it might seem counterintuitive, these tests will almost certainly decrease the number of abortions. And not only in cases of rape. These tests will also lead to more women keeping their children in cases of incest and even in some cases where a child might be conceived because of an extramarital affair.

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Category: Biology, Blog, Health

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Dr. Barry Starr

About the Author ()

Dr. Barry Starr is a Geneticist-in-Residence at The Tech Museum of Innovation in San Jose, CA and runs their Stanford at The Tech program. The program is part of an ongoing collaboration between the Stanford Department of Genetics and The Tech Museum of Innovation. Together these two partners created the Genetics: Technology with a Twist exhibition. Read his previous contributions to QUEST, a project dedicated to exploring the Science of Sustainability.
  • 1st-crackerhead

    if the entire genome can be sequenced genetic defects or sex could be options for selection

    • Barry

      Definitely a concern…

  • Jennie Dusheck

    Very cool. It's not strictly true though that any DNA that's not the mother's belongs to the fetus. Microchimerism can include stem cells from previous pregnancies and even the grandmother in some rare cases. But presumably those are rare.

    • Barry

      Very true…my fault for going for a shorter blog. Microchimerism (for those of you who might not be aware of this, see our previous answer at http://genetics.thetech.org/ask/ask375) could complicate things but hopefully would be rare like you said and if enough testing were done, it could still be distinguished from the current fetus.

  • concerned

    But is it accurate enough to hold up in court?

    • Barry

      I know that it has held up in court before although I don't know how many times.

      • concerned

        Thanks.

  • sam o

    Barry, not sure if the result would be accurate enough to hold up in court but, I think it possibility it would. Here is a link you might want to ask them http://www.4dnatransport.com.

    • Barry

      I know of at least one case in Texas where it held up. Let me find out if there are others.

  • Helen F

    Most of these tests are accurate. My cousin did a prenatal test at 14 weeks using http://accu-metrics.com/prenatal-paternity.php and got her answer. The fetal DNA in the mothers blood does exist according to whole line of literature. I would love to know which company is actually sequencing the fetal genome and whether there could be enough coverage. From what I fetal DNA is very little relative to the mothers DNA in the blood.

  • Peter Hollis

    Ultimately I think the science is robust enough to be accepted by a court, but generally the criteria for acceptance by the legal system is rarely exclusively about the quality of science, but a whole host of other factors. I'm not a specialist in this area but have a close friend that had a prenatal gender test completed at 12 weeks of pregnancy, because she was unsure about the biological father. She used a Canadian company at http://www.easydna.ca/prenatal-paternity-test.html but I'm pretty sure they operate in a number of countries according to their website.

    I was surprised at how clear cut the results are, and how easy to interpret they are. I was expecting a scientific report that would be a nightmare to interpret but that wasn't the case. Whilst the legal issues are going to be important for some, I think the vast majority of those that use the test are likely to be in the same situation as my friend. I think for the health of the mother and unborn child removing this uncertainty at the earliest opportunity can only be a good thing, and I welcome this genuinely useful advance in science.

  • PTC Labs

    There are reliable non-invasive paternity tests. They are offered by two different US laboratories and sold by a number of laboratories accredited by the American Association of Blood Banks (AABB). There is also a company (or a series of names for a company) in Canada that has offered non-invasive paternity tests for years. In our experience, they are more likely to be wrong than to give the correct answer.

    Of the fifteen tests that our laboratory has reviewed from this Canadian company in over more than a decade, twelve of the results reported by the Canadian company were proven to be wrong. In many of those cases, our conclusion was confirmed by other AABB-accredited laboratories. In two of the remaining three cases, we were not asked to retest the parties, so we simply do not know if the results were wrong. Presumably that Canadian lab gets a higher percentage than this right simply by guessing (they have a 50/50 chance). But only individuals with reason to question the original result seek a second opinion. See:
    http://ptclaboratories.wordpress.com/2013/01/09/are-paternity tests-always-right-what-about-non-invasive-prenatal-tests/

    Our laboratory is not the only one that has had this experience with the Canadian laboratory. See:

    http://www.newscientist.com/article/mg20827893.200-the-danger-of-unreliable-paternity-tests.html

    Many other AABB accredited laboratories have many examples of incorrect tests from the same group.

    In reply to the comment in the blog about the test from “Easy DNA,” the test gave the desired answer and things appear to be great. The test may have given the correct answer. There are only two possibilities after all! But if this test was performed by the Canadian group targeted by the New Scientist magazine article then there is no way to
    know. Maybe, if the test is incorrect it will never be discovered and maybe it will be apparent as soon as the baby is born. In our experience, clients who use that laboratory don't know any more after the test than before the test. They just think they do.

    People need to do their homework, but that can be very difficult. A pretty website and self-serving statements aren’t enough. If the test is not offered by an AABB-accredited laboratory, then the client should be very wary. If a legitimate laboratory cannot offer the test it, is likely that there is a reason. Questions that you should be asking are – Has the laboratory published in reliable medical journals (cites to other scientific articles is
    not adequate)? Is there negative publicity and law suits against the organization? What are the credentials of the Laboratory Director?

    No one seems to realize that there is no mandatory regulation of this industry. If you want to open a paternity laboratory in your kitchen flipping coins, you can make a pretty website and put on a laboratory coat and tell everyone you are the most intelligent and most reliable laboratory in the world. Only clients suing may stop you.

    There have been lawsuits filed and won over some of the incorrect tests from the Canadian laboratory. Some had very significant awards, but to my knowledge no one has collected a penny, and for more than 10 years the inaccurate testing has continued. When shopping for a paternity test, you can protect yourself by insisting on using an AABB-accredited laboratory, either in the United States or Canada.

  • Kate Lee

    If this could hold up in court for paternity issues, I wonder if it could hold up in court (i.e. Supreme Court) in determining the "personhood" of a fetus. One of the lynchpins of the pro-abortion arguments in Roe v. Wade et al. related to the personhood of a fetus. Interesting legal repercussions due to advances in science to come?

  • Cetin

    Hi there, I am from Germany and I am also doing this test. Here in Germany the test is forbidden, so I had to sent the test sample to Austria to http://www.confidence.at and they sent the test to http://www.natera.com
    The first time the test was unsucessful and they just wrote in the email: "The test showed Insufficient fetal DNA. Kindly redraw mother. "
    So I asked what went wrong but did not get any answer neither from Natera.com nor from Confidence.at, not even if there was too little blood in the sample.
    I am very disappointed by both companies about their information policies.
    I had to wait for another week to get an extra tube to redraw blood. This test seems to be very unreliable.

    • Ronus

      At least they were honest to admit they could not find enough fetal DNA. i would consider this as a sign of reliability (altough their communicaton may be poor indeed). Any development since then ?

  • Kristen

    I did a prenatal paternity test through Accumetrics a few months ago and it gave me an inclusion for the guy I tested. I did another one after that through DDC (who sends the samples to Natera for testing) and tested the same guy, the results came back as an exclusion. Is Natera a trusted company? I have strong doubts about the results.

  • just me

    Is Natera a reliable lab??

  • jojo
  • Pebbles

    Did anyone ever had an incorrect result by Natera/ DDC? I had a inclusion AND an indeterminate result. Now i am confused. Can i trust the inclusion?? I am due this week.

    • preggo29

      Hi Pebbles, I was wondering if you had confirm your results with DDC. I also had this test done and I'm nervous about the accuracy. I know of some others that had a good out come with this company but I just wanted your input.

      Thanks,