What you need to know about the First Trimester Screening Tests
First trimester screening is a test for genetic abnormality and is commonly called the Down Syndrome screen.The types of test, the accuracy, the costs and the ability to give you a definitive answer about genetic abnormality is really not well understood by patients…and sometimes care providers.
At times, a screening test can create more questions than answers. Firstly, it is normal to assume all will be fine. Most of us do that, right?
It can then come as an enormous shock to you if you get a result you weren’t expecting, particularly if you haven’t had a really good chat with your care provider before the test.
This test is purely your choice. What you choose to do with the results is your choice.
My hope is that we all (care providers, family, friends, community) then support your choice with respect and non-judgement.
This podcast gives some key points to help you with your choice:
What are your chances of having a baby with a genetic abnormality
How to assess your background risks
What tests are available
What are the timeframes to have each test
What are general costs
If you have just started listening to "The Kick" and are in the first trimester you may want to also listen to our most popular episode to date, Episode 5 "ALL the early pregnancy symptoms"
(If you live elsewhere in the world and have some good resources you would like to share email us firstname.lastname@example.org)
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This is Episode 13 of the kick pregnancy podcast and we're so glad to have you here listening. We are incredibly enthused by the response that we're getting from all our listeners out there and know that you can either contact us via our Instagram page @grow_my_baby, just send us a DM or we also have an email address email@example.com So this is what you need to know about Down syndrome screening. So welcome Pat.
Patrick [00:01:07] I've been looking forward to this one because in my day to day clinical practice this is something that I think is really not well understood by people. Sometimes by patients and sometimes by care providers. I think it's really important that we get this right and that we give people choice. Choice to have it, choice to not have it. If they're going to have it, which test they want. What are the pros and cons of the various tests.
Brigid [00:01:35] Because it's an optional test isn't it.
Patrick [00:01:38] Absolutely yes. So this isn't one of the ones that when you first go to a GP and say "I'm pregnant”, and they spit the thing of tests out of their computers and say "go and have this blood test”. This is not on there. This is a separate different one.
Brigid [00:01:50] Yeah. And about 80 percent of women choose to have a Down syndrome screening test.
Patrick [00:01:56] They're not for everybody. But yeah, the Victorian figures are about 80 percent.
Brigid [00:02:00] All right so you mentioned that there's a couple of different tests that we can choose from perhaps if we talk about the first one?
Patrick [00:02:08] Yes. The one that was is still in common use and was certainly in very common use when I first started in obstetrics was something called a combined first trimester aneuploidy screen. The word aneuploidy means the wrong number of chromosomes. So, for our purposes today we'll talk about it being for Down syndrome screening. Down Syndrome, of course are three copies of chromosome 21 but there are some other chromosomal disorders that are also tested for by these tests.
The combined first trimester screening involved having a blood test at 10 weeks and an ultrasound at 12 weeks that measures the thickness of the neck of the little foetus and the woman's age.
Patrick [00:02:54] And those three pieces of information would be fed into an enormous computer database where hundreds of thousands of other pregnancies have already been considered and your results are compared to the results of other people where the outcome is already known.
Brigid [00:03:10] And it's hard because it all seems to be kind of about probability and on of that, how common are these diseases?
Patrick [00:03:16] Well if we look at Down's syndrome as a good example, it depends on the mother's age and there's no doubt that Down's syndrome is much more common when the woman is over 40 at the time of conception. But there aren't that many women over 40 who are conceiving in the first place. So even though the risk of Down's syndrome goes up with the woman's age, most women who have a pregnancy affected by Down's syndrome are in their 20s because those women are having most the babies right. Does that make sense.
Brigid [00:03:49] Yes. So is there a number we can put on it?
Patrick [00:03:52] Well you background risk in your 20s might be in the order of 1000. And the background risk when you're 44 might be in the range of one in 50.
Brigid [00:04:01] Right. Well yes that's a big difference?
Patrick [00:04:02] Enormously and women are much less likely to have a baby at 44 than 24.
Brigid [00:04:07] Yes that's right. Well it's important for all ages to consider this test or do you think it's more specific to a particular age?
Patrick [00:04:17] Well I think that it's something that should be offered to absolutely everybody because everybody's at some risk. And I think also it's up to the woman it's up to the couple what they consider to be an acceptable risk for them. Yeah. Okay. We shouldn't be telling people what to do in this regard. So even if we've got someone who's pregnant and is 21 whose background risk, (background is the risk carry before you're ever tested). Okay. But their background risk might be very low. But it's not zero. And for that person having a test might be the right thing to do.
Brigid [00:04:47] Yeah. And so why would some people choose not to have the test?
Patrick [00:04:51] People might choose not to have the test for reasons of expense and also for reasons of their attitude to for example the termination of pregnancy. So one of the reasons why we might test for some of these disorders is that some people say well if I'm carrying a baby that's got x y z genetic condition then then perhaps I'll have a termination of pregnancy. And if someone feels that they wouldn't have a termination of pregnancy under any circumstances then they might question the wisdom of having the test in the first place.
Brigid [00:05:21] And someone might choose to have the test and know that they wouldn't terminate the pregnant yes but it helps them to prepare for the birth of a child with Down syndrome.
Patrick [00:05:30] Absolutely and I've certainly had this scenario once or twice in my career where people have said "I had the test because I wanted to know and obviously I was looking for a normal result. But now that I don't have a normal result, I'm still going to carry on with this pregnancy but I'm going to go and join the Down Syndrome Society and I'm going to prepare, we're going to make some decisions as a family about what having a special baby is going to mean for us.
Brigid [00:05:52] So what sort of counselling or discussion happens with your care provider before you have that test or what should your care provider be talking to you about?
Patrick [00:06:01] I worry that it's not much that's going on out there like a lot of tests. We just assume it'll be fine and it can be an enormous shock to people if it's not. You know one of the most well-known, non obstetrics is HIV testing out there in the real world. Theoretically if you're having an HIV test you've probably had some sort of accidental exposure or it's some sort of risk - or you wouldn't be having the test in the first place. And we probably should be having a talk about what we can do if it's positive. Absolutely. So if you if you look at pregnancy I'm sure we don't do enough discussion about what are we going to do if this is positive but is there any way to prepare someone for an abnormal result. I don't know.
Brigid [00:06:43] Knowing perhaps what they would do with the answer is important.
Patrick [00:06:48] Well that's what I do for people. I mean when they're thinking about “will I have the test or not” I'll sometimes ask them, "Are there any circumstances in which you would consider termination of pregnancy?” and if they say yes, it's all fine have the test. Yeah. And of course, cost is a block to some people these and these are not funded tests that cost money. Okay.
Brigid [00:07:07] So do we know how much. Yeah.
Patrick The first trimester combined one, that the first one we were just talking about it cost about $200. Right now, these are not usually done as a funded test through a hospital - even if you're a public patient in a public hospital - they're not normally giving people a slip for this test. Much more commonly you would go to a local doctor say I'm pregnant they give you a form saying, "All right we're gonna have the usual first trimester blood test the one with the blood group, haemoglobin, rubella status, Hepatitis B, HIV syphilis and we've discussed that another day (this is episode 4). And then the local docs might say well we're going to send you to the public clinic for your baby but you’re not going to get in there till you're 17 weeks, so go and have a first trimester combined screening. Yeah but there's a bill in pathology collector that the laboratory that puts it all together and spits the answer out and the ultrasound provider.
Brigid [00:08:00] Yeah. That actually raises a good point too. So when do I need to have this test by.
Patrick [00:08:05] Yes so this one is 10 weeks for the blood's. 12 weeks for the what's called the nuchal thickness, which is basically the thickness of the baby's neck on ultrasound and then you get the result at about 13 and a half weeks.
Brigid [00:08:18] Yeah. So for those women that are perhaps going through the antenatal clinic at a public hospital or something and as you pointed out might not be there until 17 weeks. Yes. It's off their own bat isn't it. Yeah.
Patrick [00:08:30] You need to know about this, and you need to be advised about it and and get this organized first. If you wait for your first visit in the clinic it's too late.
Brigid [00:08:38] Yeah you might have just missed that window. Yeah.
Patrick [00:08:40] Well we see people who haven't been screened.
Brigid [00:08:43] Right. And then feel like they haven't been given the right sort of information.
Patrick [00:08:47] Yes. And whether you know is that the system? I think is more the system's fault. But then of course the patient blames themselves.
Brigid [00:08:54] Yeah. So in all circumstances does this test work?
Patrick [00:08:58] Well no this isn't a yes or no answer. This test. It comes out as a risk. So if we look specifically again at the Down syndrome risk, it will say something like in this woman the risk is one in 10,000 which would be great or it might say the risk is 1 in 10 which would be bad. That's high risk. Yeah. And where's the cut-off. It's an interesting question where the cut-off is because to a certain degree it depends on a woman or a couple’s perception of risk.
If you think that if I told you that the risk of Down's syndrome for your pregnancy was one in 300 there are some people who go beauty that's really low, it'll never happen. And there are other people who say that's too high that that'll be me. I'll be the one. Yeah. Yeah. And some of that is the sort of bias that we bring into it in the first place.
Brigid [00:09:49] I'm not I'm not comfortable with a one in 300 and I would need further testing for that. Yes. You know that's my personal sort of risk aversion.
Patrick [00:09:56] So most people have a sort of a cut-off of around that one in 300 sort of mark to say if it's higher than that. Okay like one in 200 one in 100 that we should be doing further testing and that's in the form of an amniocentesis.
Brigid [00:10:12] So can you just tell me what an amniocentesis is?
Patrick [00:10:16] My amniocentesis is a way of finding out for sure. And it's a procedure done under ultrasound guidance where the amniocentesis, the doctor passes a small needle through your belly into the water around the baby, under ultrasound guidance so they don't hit the baby, and they suck some water out from around the baby. And in that water there are tons of skin cells that have come off the baby. And then they can be analysed by direct DNA analysis to say yes or no. Yeah. Right. And that's what we call the gold standard. That's is essentially a 100 per cent reliable yes or no answer.
Brigid [00:10:56] Yep. And if you're looking for something to help you base a decision about termination for example, do you have to go and have an amniocentesis. Yes.
Patrick [00:11:06] We don't advise people on termination of pregnancy for example on a first trimester combined test that says the risk is 1 in 10, even if we strongly suspect that it's actually a positive test. Because that's not what a screening test does. So a screening test is a bit like a pap smear it doesn't tell you what's wrong, it's the biopsy of the cervix that really tells you what's wrong. So a screening test is done on a healthy population to try and find people at risk of a problem but it's not a diagnostic test. So if you get a high risk first trimester screening often have an amnio and that's what we go off. And why don't we just do the amnio first place? There's risks involved. It's really dear. And people don't want to stick needles in their pregnancies. No.
Brigid [00:11:51] All right. So what happens though if I've say got to 14 weeks and I've probably missed my boat. What can I do to find out whether my child might have Down's syndrome?
Patrick [00:12:02] Well there are other tests that can be done. So we should discuss those. So you've only missed the boat for that one particular test. Okay. Yes there is a thing called a second trimester screen which just uses the blood tests alone. It's got problems with reliability but it is available and it's better than nothing. No problems with accuracy but in my view the best of them all is something called a NIPS test which is non-invasive prenatal screening.
Brigid [00:12:29] Yeah which some people refer to as the Nips test?
Patrick [00:12:32] Or there is a brand name Harmony test. Right. And a lot of people know what that is. Yeah. So this is the best of the screening tests.
Brigid [00:12:42] So it's still a screening test though?
Patrick [00:12:44] Yes it is, but it's an incredibly reliable one. Okay. So it can be done from 10 weeks. So it's often done in conjunction with an ultrasound but you don't need an ultrasound and it's just a blood test from the mother. Totally different technology.
We've known for a long time that in pregnancy a small amount of cells from the baby, or more accurately from the placenta, have broken off the placenta and are whizzing around in the woman's circulation. And we've known those cells have been there but it's only relatively recently that we've been able to catch them and sort them out from the zillions of the woman's blood cells that are in there in a blood sample and identify the fetal ones and analyse them.
Patrick [00:13:30] It's amazing technology so that that's been available I guess in Australia for about eight years something like that.
Brigid [00:13:37] And what chromosomal abnormalities does it actually pick up?
Patrick [00:13:41] Well it can pick up the big ticket ones like abnormalities of chromosome 13 18 and 2, so three of the more common ones and it can do gender as well. Right. So because they've got some actual DNA to work off they count up X and Ys. Yeah. And that gives gender.
Brigid [00:13:59] And so how accurate is it for gender?
Patrick [00:14:02] It's very accurate for gender, about 99. Right. And the error rate for that for say Down syndrome is about one in ten thousand.
Brigid [00:14:09] Yes. So because of that error rate I'm assuming that you still have to go and have an amnio?
Patrick [00:14:14] Yes you do currently. Yeah.
Brigid [00:14:16] So how do I get this test?
Patrick [00:14:18] Well this is one that needs to again be organized through local doctor or through obstetrician and it costs more money again. So about $400. Right. And if it's done in conjunction with an ultrasound it might be a little dearer than that as well.
Brigid [00:14:33] Yeah I don't understand, why do people even do ultrasounds if it’s not necessary?
Patrick [00:14:38] Oh well you might just have an ultrasound at the same time so that they can have a look at all the rest of your baby and make sure it doesn't have any structural abnormalities because you could have a fetus that was highly structurally abnormal but still genetically normal. Right. Does that make sense. So the the NIPS screening test might be falsely reassuring. Right. So if you have an ultrasound as well and everything looks right the bits and pieces are all there. Babies got normal head, normal body and so forth then that just add some further reassurance to the normal and obvious result.
Brigid [00:15:15] All right. So I'm a bit confused if both end up giving you a high risk and then both have the next step of needing an amniocentesis kind of anyway. Why wouldn't I save my money and just do the first trimester screening?
Patrick [00:15:28] Because the NIPS test is more accurate. So if NIPS says that there's nothing wrong there's almost certainly nothing. Right.
Brigid [00:15:37] Okay. Whereas the first trimester screening might give you a false negative.
Patrick [00:15:42] There’s a false negative and there are false positives. And in general terms the NIPS is more accurate overall.
Brigid [00:15:51] I'm gonna really pin you to a decision here so I'm a bit over making decisions. I'm also feeling quite sick in my first trimester, as an obstetrician, what will you recommend me to have?
Patrick [00:16:01] I think the money spent on an NIPS test is some of the best money you'll spend in pregnancy. Right.
Brigid [00:16:06] Okay so you send most of your patients to all of them?
Patrick [00:16:09] Yeah but pretty much all of them. Yeah. This is a big ticket item for people. It's not a discussion about whether you would or wouldn't terminate a pregnancy with it with an abnormality. It's about people's desire to know that things are okay and a 10 week normal NIPS test it's going to rule out some really big ticket problems. Yeah. And and then if a problem is found another advantage of NIPS compared to combined first trimester is that you'll get the result usually within a couple of days. So if there's a major problem you will know right at the start of pregnancy when it could be confirmed early. And if you did want to proceed to termination of pregnancy, the earlier the better.
Brigid [00:16:59] Yeah. Whereas the first trimester. I'm hearing that you have the first blood test at 10 weeks after the ultrasound at twelve weeks and then you probably wait wait a couple of days.
Patrick [00:17:08] Yeah it takes it takes longer for the result to come. So that you might get that result at 13 1/2 and then you get amniocentisis organized. Well you might not have the full confirmation till 15 or so weeks away. And you're more out into that territory where if you did want to have a termination of pregnancy that would be by induced birth. Rather than a surgical termination of pregnancy whereas what we've been looking for for many years is a highly accurate, highly reliable test that can be done early in the pregnancy, so that God forbid there was an abnormality, and we can say to that couple you know if you want a termination of pregnancy on the basis of that it can be done at an earlier stage of pregnancy which is overall less traumatic.
Brigid [00:17:55] All right. So I'm going to have an NIPS, if that was me. I'm not going to have any more babies but if that was me it would go down and have an NIPS test. So I would go to my GP, or probably my GP. You probably haven't started seeing it obstetrician yet?
Patrick [00:18:07] Well one of the reasons I see my new patients right on 10 weeks is so that if they haven't had one, I can organize it.
Brigid [00:18:13] So I go to my GP and they give me a slip to go and have a blood test at the local lab. Okay. And I pay the money there. Yep. And then I just wait.
Patrick [00:18:22] Yeah. And they'll inform you of the result. Usually within a few days. All right. In the very early days of this it was only available in America. So it was firstly commercially available in California. So we were doing it collecting the blood they'd send it on a flight over to a lab in California and they would do it and then email back the results.
Brigid [00:18:44] Actually this raises that point. So yes, labs are a commercial operation. And quite often people think that doctors recommend things because there's some kickback or some affiliation but we're just here to say that there's no affiliation with any of these medical labs are there?
Patrick [00:18:59] No. The guys who run first trimester screening is the Victorian clinic genetic service and they're part of the Royal Children's Hospital. So I mean they charge for their time and they charge for the cost of providing the test and then the NIPS providers. There's a few of those and they're in commercial labs which are private companies and we want them to be in more labs to drive the price down.
Brigid [00:19:21] Drive the price down that'd be fantastic wouldn't it? And can someone shop around?
Patrick [00:19:25] Yeah you can shop around and ask a few providers. So but what I'm hoping is that as the NIPS cost approaches the cost of the other test, we will stop doing the other.
Brigid [00:19:38] Yeah. And wouldn't it be great even if it was funded?
Patrick [00:19:41] Well it would be great if it was funded there's some interesting politics behind all of that but that's not yet.
Brigid [00:19:46] No. All right everyone. Well I think we've covered the first trimester screening for Down syndrome if you haven't already please subscribe to our podcast.
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