First Trimester Screening

Here is a news article discussing the inaccuracy of first trimester screening.

This test has a 95% false positive. So for every 3 normal babies a downes syndrome baby goes to term, whilst 40% of all downes syndrome baby’s are missed altogether.

Why then is this test held up as the pinnacle of diagnostic tests? I was talking about this article just yesterday with a midwife who said that she thought it was supposed to be the most accurate test available. If midwives think this then what are the women led to believe?

What is the motivation for this test? Many women just go along for the test because it is available and seen as a normal part of pregnancy. No thought goes into the potential catastrophic change in the pregnancy that a positive result can bring.

Before considering any test the end result should be considered. If you are testing to find out if your baby is “perfect” then you must be prepared either for losing a normal baby or decision making surrounding a positive result.

Most women would quite happily travel along with little or no thought about this if the test wasn’t available. However, even a test with a 95% failure rate and possible fatal outcome for the fetus seems to hold an irresistible pull for practitioners and women alike.

Women need solid information on antenatal screening so they can make an informed decision on the progress of their pregnancy.

12 responses to “First Trimester Screening”

  1. Amy Tuteur, MD

    “Women need solid information on antenatal screening so they can make an informed decision on the progress of their pregnancy.”

    They aren’t going to find it here. I have been following your blog and it is a festival is mistruths, half truths and outright deceptions. This post is a case in point. Ultrasound does NOT have a 95% false positive rate (do you get all your scientific data from newspapers?). According to an article in the March 2008 issue of Clinical Obstetrics and Gynecology, entitled The Use of Nuchal Translucency in Contemporary Obstetric Practice:

    “Nuchal translucency sonography is the most powerful single prenatal marker for Down syndrome. Its detection rate is 75% at a 5% false-positive rate. The combination of nuchal translucency and maternal serum-free [beta]-human chorionic gonadotropin and pregnancy-associated plasma protein-A can identify 85% to 90% of fetuses with Down syndrome for a false-positive rate of 5%. This method can also identify more than 90% of fetuses with trisomies 18 and 13, Turner syndrome, and triploidy for a screen-positive rate of 1%.”

    If you are really a midwife, you have an ethical obligation to provide accurate information and not simply make it up as you go along. Please take that obligation seriously.

  2. Lil

    That’s a really interesting point you make! We had a nurse/geneticist come out to talk to us at uni. She was saying how important she felt it was to offer counselling to ALL women before ANY screening test (such as ultrasound). (That is of course in an ideal world!!) I think a lot of women don’t really consider what they would do if their result wasn’t what they expected.

  3. Lisa Barrett

    Thanks Lil, it’s always about choice.

    Dr Amy,
    It’s wonderful to hear you are such an avid reader of my blog. As we all know the medical profession are exemplary at telling us the truth, second only to governments no doubt, so I welcome your learned opinion openly.
    In this state (South Australia) I am vice president of the SA College of Midwives and sit on the Neonatal and maternal outcomes steering committee. There is a debate about this screening statewide, as none of the 3 tertiary institutions actually offer the test. Women have to access it privately through their GP. One of the large hospitals feels that it should stay that way due to the cost and effectiveness being issues. As you see I don’t come from a place of mistruths or deceptions.
    this is a midwifery site, which is full of accurate facts and my own opinion. I hope you continue to read and be enlightened, it may even go some way to lifting that chip off your shoulder.

  4. Amy Tuteur, MD

    lisa barrett:

    “which is full of accurate facts”

    Hmmm. You made a claim that was completely false. You referenced a newspaper article. You have no objective evidence to put up against the scientific paper that I cited.

    I don’t doubt that you have trouble telling the difference between fabricated falsehoods and facts. I just want to warn others that you are spreading midsinformation.

    “I am vice president of the SA College of Midwives and sit on the Neonatal and maternal outcomes steering committee.”

    Then you have a legal and ethical obligation to educate yourself about the scientific facts instead of copying junk from the local newspaper.

  5. Lisa Barrett

    ” Its detection rate is 75% at a 5% false-positive rate. “

    Taken from the abstract which is all I have available to me. If you’d like to pass on the full text that would be lovely.

    detection rate is 75% false positive is at least 5%. so at least 20% of babies are missed.

    Even if the newspaper wildly exaggerated the facts it’s still not looking like a particularly accurate test.

    Input of opinion different to mine is appreciated, as choice is made by looking at lots of facets of research. However personal insults on my blog are hardly professional or ethical. Further comment is invited without this.

  6. Lisa Barrett

    Dr Amy sent a comment, unfortunately I’ve decided not to publish it due to the demeaning tone. She did however make a very good point.


    Many screening tests have false positive rates that are far higher, but this is deliberate. The purpose of a screening test is NOT to make a diagnosis. It is only to flag people who are at risk and, therefore, are candidates for the diagnostic test.

    We are aware when a screening test has a high false negative rate. That’s why we offer women the option of amniocentesis (the diagnostic test for chromosomal problems) even if the screening test is normal.

    Telling women that there is no point in having prenatal screening tests is like telling women there is no point in having PAP smears or mammograms.

    To recap, claiming that a screening test is not highly accurate is simply stating the obvious. They are designed that way deliberately, and they are designed that way for a very good reason. It is the diagnostic test that must be highly accurate, not the screening test.

    Thank you for this input. It’s always good to understand the medical point of view.

  7. Maddy

    As a nurse in OB/GYN, I’ll just say that we really have to be honest here. Dr. Amy thinks its perfectly fine to have an outrageous false positive rate, which needlessly stresses people out and may even result in a miscarriage after unecessary invasive diagnostics. Have you ever sat and talked to a woman who is breaking down right in front of you because her twin boys were lost during an amniocentesis? I have seen it time and again, and this is not good medicine- it is the eugenics movement. It reeks the odor of Nazi Germany- and we said it would never happen again!

  8. rosie h

    hello, as a GP and homebirth advocate who happened upon you site whilst doing some research i feel compelled to comment. I had a homebirth midwife for my own birth and had no antenatal testing of any kind including ultrasound. This was because i felt clear about my informed decision. I am a firm supporter of women’s informed choice. I am a firm supporter of midwives. I am exasperated by divisions into ‘doctors’ and ‘the medical system’ as if they were the bad guys whilst midwives/natural medicine are all good. the reality is there is plenty of good, and good people in medicine. we all know where we would want to be with a very complicated delivery with no delivery after 3 days and lots of thick meconium and a failing foetal HR. hospital.
    on the other hand, in a staight forward pregnancy home is a brilliant choice. and there is no doubt that some in medicine do give misleading messages about risk. however, it stands that your comment about 95% false positive rate for down’s syndromw testing is frankly wrong as any research of the papers will show. the false positive rate is around 5% and probably around on average 85% downs are picked up. whether or not that rate is acceptable to you or whether you consider this to be eugenics are separate matters, and part of a personal decision making process that should be respected. as long as each woman having this test understands the implications and outcomes and still feels that she wishes to have the test, we are doing a good thing. lets all work together to get the correct information, free of bias, to pregnant and birthing women to allow them to make their own informed decisions and birth in their own power.
    i think the comments about amy’s post have been a bit over the top. she is right about your information being wrong and you are wrong to say she thinks an outrageous false positive rate is right. we are all working with the best tools we have.
    may all women give birth as they wish, in the safest and most deeply nurturing way possible.

  9. Anonymous

    I ran across this blog and find it interesting. I am a family physician and deliver babies in the U.S. and teach family practice residents. I think the issues here is that people are getting false positive and negatives mixed up. The first trimester screen is a pretty good test at detecting most trisomy 18 or 21 fetuses at an early age. As determined by subsequent diagnostic tests such as CVS and amniocentesis. But as a screening test, most women who will show an increased risk of problems, will actually have normal fetuses (I think that is where the 95% false positive number comes from)

    Because of this, I always ask my pregnant women, what would you do with the results? and how would you handle the anxiety that may come from an abnormal screening test. That way, they can truly make an informed choice. If they would not think of terminating the pregnancy or would not want CVS or Amniocentesis with their small but appreciable risk of miscarriage then perhaps the test is not for them. Also, if they do not want to deal with the anxiety of a potentially abnormal screening test, then don't get the test!!

    Using this approach I would say that probably only 10-15% of women that I counsel actually opt for the test.

  10. Anonymous

    Wow isn’t Dr Amy just the epitome of the God Syndrome!! You, Dr Amy, are why I want to birth at home!
    Have you ever thought about WHY you are doing all these pre-natal tests? Have you asked each pregnant lady if she wants a late-term abortion if her baby is not perfect, or has Downs Syndrome? And what, may I ask, is the problem with that? Geez if we scrape all the alleged non perfect babies, where will all the compassion be in the world?
    Dr Amy, I am now going to visit YOUR blogs, and see if I can make rude, uninformed comments on there!
    By the way, you are in the USA, and we all know the issues over there. You also have the dubious honour of having what is it, the 3rd highest infant death rate at birth? Forgive me for not knowing the medical terms.
    So take your scan and shove it where the sun don’t shine I say! And isn’t it about time you retired? Oh hang on, your american, so no. You my dear god-like OB-GYN will be unfortunately practising until you are 75 when you might be able to retire.
    Why is it that the negative comments come from oh, medical MDs? Gps? Whatever. You’re not birth specialists for NORMAL BIRTH. You should also be ashamed of yourself, making bullshit comments on an informative, excellent blog. Why follow it then if you dont believe it. TROLL.

  11. Elizabeth

    Be really careful with pap smears during pregnancy and 6 months after delivery.
    The odds go way up at these times and you’re more likely to get a false positive. This can be really worrying. My poor SIL spent her entire pregnancy worried sick and all for nothing.
    The risks have been known for sometime but many doctors carry on regardless.
    There is a great website that seeks to inform women – Cancer research UK – Pregnancy and Abnormal Pap Smears.
    The trauma of childbirth can produce abnormal pap smears and the hormonal changes during pregnancy.
    Most women don’t have the facts about this screening. There are two great websites that seek to inform – Dr Joel Sherman’s patient privacy (Women’s privacy concerns parts 1 to 5) and Violet to Blue.
    Hope this helps some of you.