Blood test screening in pregnancy
The purpose of blood tests in pregnancy was a common source of confusion for the women we spoke to. Blood tests are carried out for many reasons'
- to check the mother's blood group
- to monitor the mother's health (for example checking iron levels for anaemia), and look for conditions which may develop in pregnancy such as diabetes and pre-eclampsia
- to screen her for conditions she may already have which can affect her or the baby (such as HIV or various sexually transmitted diseases)
- to check whether the parents are carriers of inherited conditions such as sickle cell and beta thalassaemia (see our website on 'Screening for sickle cell and beta thalassaemia')
- to screen for immunity to infectious conditions such as rubella which can harm the baby if the mother catches them while pregnant
- to screen the baby for conditions such as Down's syndrome.
See also 'Resources' section of this website.
Here we concentrate only on tests which screen for conditions in the baby, but many women we talked to were not very sure why their blood was being taken (see 'Information for making decisions').
- Age at interview:
- Children' 2 (aged 5 and 2), Occupation' NCT teacher, Marital status' Married.
We hadn't really discussed what screening we would have. The first, with my first child I had what was on offer, which was the 20-week scan, and that was it basically. I probably had AFP [alpha-feto protein] blood tests, various things like that, but I don't know that I was actually aware I was actually being screened, because it is just what you do.
Not everyone worried about this, and some happily trusted their doctor or midwife to act in their interests. One woman was concerned that her results were taking a long time to come back, including the tests to see if she was a carrier of sickle cell disease.
- Age at interview:
- Children' First pregnancy, Occupation' Mother - student, Father - student, Marital status' Married.
I don't know everything that they take. I mean I know that they're, the first time that I went to this private doctor, he tested for all sorts of things. I mean all sorts of diseases and whether I had antibodies to certain things. So I knew that there were just a bunch of tests being done at that point.
Since then, I know that they check, with me they check for specific things, like they check my thyroid every couple of months just to make sure that it's doing all right. And I know that they checked at one point, they double-checked my blood type. I guess that that could be a problem or at least something that they want to make certain about.
Did you have a leaflet or anything saying what all the blood tests were for?
No, I didn't, but I do have my chart, so I can see actually as the results come in what they've checked, so there's a little bit of, you know, evening's reading can be, 'What have I had done last week?' But no, I haven't had any sort of information. I think that there is a certain degree of just trust, you have to trust that the person is checking for the right blood things and doing the job that they're supposed to be doing.
- Age at interview:
- Children' First pregnancy, interviewed when 7 months pregnant, Occupation' Mother - nursery nurse, Father - telesales worker, Marital status' Single, partnered.
Yeah, I had eight of them taken and she explained what some of them were for, to check for rubella, my blood count cells, I think it was, and to check for the Down's syndrome and other things. I also had a problem with that though, because I only got my results last month back.
Because normally you're meant to see the midwife and she was meant to, every time she went to get my results she couldn't see anybody. So it's only, I - well, she said that 'How come you haven't got your blood?' And it should be written in the back of my book and it wasn't, so she had to keep on chasing them to get it back.
So when she did get it back she did go through it with me. I had to, I asked her about it, and my red blood cells are low and my iron is low, so I'm taking iron tablets at the moment now, but that could have been done ages ago if they had - you know, because I took these blood results in July and we're in January now.
And is that also the case with the blood test for Down's syndrome risk, that came back late?
No because it was taken the same time I had these - but because there was, they sent it in the post I already got that anyway, so I knew about that, so that one wasn't a problem. It was just my blood results that I didn't get back.
And what about sickle cell, thalassaemia - have you had screening tests for?
That was also done the same time as well, but I haven't had any results back about that. I haven't had any results back on that neither.
Footnote' A separate DIPEx site on 'Screening for sickle cell and beta thalassaemia and other haemoglobin variants' is also available.
Not everyone was aware they could have a blood test around the same time as their nuchal translucency scan, to produce a combined and more accurate risk assessment for chromosomal conditions, especially Down's syndrome. The NHS Fetal Anomaly Screening Programme now recommends that women have the combined screening for Down’s syndrome (blood test and nuchal translucency scan) rather than just the blood test or the nuchal translucency scan on their own. The vast majority of units in England, Scotland and soon Wales now offer combined screening for Down’s syndrome.
One woman told how her first sample was damaged and the test had to be repeated.
- Age at interview:
- Children' First pregnancy, Occupation' Mother - research scientist (trained as doctor), Father - software engineer, Marital status' Married.
My experience was very good, my GP immediately gave me all the information necessary to get, for the primark test, the blood test associated with a scan. I didn't know about it because I wasn't sure exactly what was available. I knew about the amniocentesis and all that, but I suspected that there must be other options.
So I was quite happy to hear that there was this very early test that can tell you about Down's syndrome and other common problems. So immediately I, you know, applied for that. I called myself. There was a bit of a delay, because this was in summer, early summer - very hot weather. And they send you the tubes to get the blood sample taken.
So I got the blood sample, sent it in the post, and it apparently didn't get there, or it took three days or something to get there, and they told me, 'Sorry, but this sample is not useful any more, it is too hot'. So I had about one or two days limit to send the sample right in the time when it had to be tested, because it's a very short period when you have to do this test.
So, but anyway, it got there. We were travelling to my country, to Ecuador, in the few days after that, so I had the scan, I think, just the first or second day of my thirteenth week, which was just about when it had to be taken, because we were leaving two days later.
So by the time we left I knew the results from the blood test, but not, I knew the results from the scan, which was quite good, they told me that the risks were much lower than expected for my age, but I didn't know the results from the blood test because it was not ready yet.
But when we came back we received the news that, together, the two tests together gave a risk of one in fifty thousand, so that was kind of, you know, fantastic, because then basically there was no need to go for any further tests.
One person said she had missed the test because her fear of needles had led her to delay it. For another couple this blood test turned out to be crucial in detecting Turner's syndrome, which the scan alone would not have picked up.
- Age at interview:
- Children' First pregnancy ended at 17 weeks, Occupation' Mother - opera singer, Father (age 42 at interview)- chartered surveyor, Marital status' Married.
We were trying for about four months. And became pregnant. But then I had a lot of problems. I bled for thirty days, so we had tons of scans to check for miscarriage but it had all stopped by the time we went for our 12 week scan and - which was our second wedding anniversary.
And so they did the non-invasive tests, which at our hospital is nuchal fold, age ratio and a blood test to give you a combined risk for trisomy 21, 13 and 18. And our testing came out a 1 in 32 chance for Down's syndrome - that's what it flagged under. The blood test alone at our hospital said 1 in 6. So they recommend anything under 300, 1 in 300, that you go on for a CVS.
And with Turner's syndrome it usually, the physical symptoms start in the second trimester, because that's when the oestrogen is needed. And if you're missing your second sex chromosome you don't have any oestrogen, and that's when things start going wrong. And swelling and cystic hygromas, fetal hydrops, heart problems, all of those things show up later.
We feel actually fortunate that our hospital was able to pick up so early, because the nuchal fold came out fine. A lot of times actually with Turner's syndrome it will show a raised level of nuchal fold, but it was our blood test that actually flagged it.
An alternative blood test - which people are often advised they do not need if they have had a nuchal translucency scan with blood test (combined screening) - is the quad (or quadruple) test which checks for proteins and hormones in the blood. The quadruple test measures; hCG (human chorionic gonadotrophin), uE3 (oestriol) and AFP (alpha fetoprotein) and the hormone inhibin-A. The quadruple test is now offered if a woman is more than 14 weeks pregnant and has not had a nuchal translucency scan. In the past the triple test (testing hCG, uE3 and AFP) was also used but this is now no longer offered. AFP levels in the blood were used in the past to screen for spina bifida and other neural tube defects but spina bifida is more commonly diagnosed during the ultrasound scan carried out around week 12 of the pregnancy or, more likely, during the anomaly scan carried out around weeks 18 to 21. Several people we interviewed, who were offered the triple test at the time, did not realise that measuring these substances can assess the risk of neural tube defects and one woman described how she turned down this test believing it was only for Down's syndrome. Her baby was later found to have a neural tube defect.
- Age at interview:
- Children' 1 (age 17 months), Marital status' Married.
The blood test was, the option was a double test for Down's syndrome risk and spina bifida, and it was explained to me that the results would be presented in the shape of a ratio for Down's syndrome and just in a pure sort of high or low, or normal or high outcome for spina bifida. That's what my understanding was.
So they didn't give you a 1 in 389 kind of ratio?
Not for the spina bifida. The ratio, I was expecting a ratio for Down's syndrome, yeah. And I think she explained quite carefully that I would get a letter telling me whether the result, what the outline result was and I could then phone up to find the specific ratio on the Down's syndrome but that it wouldn't be in the letter itself.
And that if there was any, I remember her saying, “We'll come knocking at your door if there's any cause for concern”. And I found that quite surprising. She meant they would physically come round and contact me in person face to face if there was any very high risk shown.
Because I found that quite an interesting way of midwives spending their time chasing round trying to find a woman who in my case, you know, might be at the other end of the country with work.
If you have had a result from a nuchal scan and blood test, it is advisable not to have the quadruple test as well, because it will also give you a risk for Down's syndrome and having two different assessments can be confusing.
After ending a pregnancy for a serious chromosomal condition (Edwards' syndrome), one couple decided against blood tests in their next pregnancy and relied only on scans. This was because the risk would automatically work out higher, because previous Edwards' syndrome is added as an extra risk factor, and they knew they did not want any further diagnostic tests. This time they felt better informed to make a real choice.
- Age at interview:
- Children' first pregnancy ended at 15 weeks, Occupation' Florist, Marital status' Living with partner.
And by that stage I'd, I thought it was past the CVS stage but we were getting into discussions about blood tests and whether I would have blood tests or not. And I said, 'Well, I think I need to talk to somebody about blood tests.' And me and my partner had spoken about blood tests, and we were both unsure about what the position, how to go about it and how we both felt.
So this midwife, who works very closely with the consultant, took us into a side-room and we talked about the blood tests, and the major thing that came out of it was that my previous history would go down and would be counted. They couldn't do blood tests without using my previous history, which I wasn't happy about.
And the other thing that came out was that if we had blood tests we were, in fact, making a choice to have amniocentesis because the results would come back high risk, more likely than not, because of my previous history. So we weren't deciding to have blood tests or not, really. We were deciding to have amnio. And as we'd already decided not to have CVS we both felt that we didn't want to have the pain and the stress of going, having amnio. So, really, we've just relied on scans throughout this pregnancy.
Do you feel comfortable with that decision?
Totally, yeah, totally. I think sometimes it's just assumed that you'll have all these blood tests, and you'll have this and you'll have the other, and I don't think there should be any assumption. I think that you should be made aware that it is totally, it is a choice. You don't have to have it.
There are so many things that you have to do in pregnancy, like blood pressure and urine samples, and you just think the blood test is just another one of those things that you have to do, and it's not necessarily true. I mean, certainly with me, having, just talked through the process of having the screening tests, I didn't realise that it would be, I was making a choice to have amnio, basically. Because I knew it would come back high risk and I didn't want that stress on myself, really or the baby. You know, I just didn't want that stress.
Another woman who had ended a pregnancy for spina bifida also relied only on scans in her next pregnancy. She felt she would have to wait anyway for the 20-week scan to know how severe the condition was, and the triple test might make her anxious unnecessarily.
- Age at interview:
- Children' First pregnancy ended at 20 weeks, Occupation' Mother - child minder, Father - upholsterer, Marital status' Married.
When I first went to see her, I was so desperate for all the tests going. Which she explained to me that the triple test at 14 to 16 weeks, I think, I could have if I desperately wanted it, although the results for spina bifida was, there were high false negatives and high false positives, that if I got a false positive and I would be so worried then until I had to go for my scan to find out if the baby had spina bifida, that I would probably just sink into depression if I had that test.
She said she would do it if I were desperate for it, so I came home and thought about it and thought that she was right. If I had a test at 16 weeks and they still had to wait till 20 weeks to find out how severe the problem was, I would still wait because I wouldn't want to terminate the baby at 16 weeks having not known how severe the problem was. So I decided then against the triple test.
Non Invasive Prenatal Test (NIPT) is another screening test that can be used to detect Down's syndrome. It is a non-invasive test using a maternal blood sample to test free-cell fetal DNA. During pregnancy, fragments of DNA from the placenta called free-cell fetal DNA circulate in the mother’s blood steam. These DNA fragments (CFFDNA) can be genetically tested along with the mother’s blood to show if there is an increase in the number of abnormal chromosomes. This screening test is not currently offered by the NHS, however some NHS Trusts have piloted the test and a number of maternity units do offer testing privately. The sample has to be sent outside the UK for analysis so the results take about two weeks to come back.
The cost of the test varies between clinics (£350 to £550£500-900). Large scale studies show that the test has a detection rate of over 99% (ARC July 2017) and also tests for some other common chromosomal anomalies; Edwards syndrome (trisomy 18), Patau syndrome (trisomy 13) and Turner syndrome. It can be performed from 10 weeks of pregnancy and unlike amniocentesis and CVS has no risk of miscarriage. However if the NIPT gives a positive result, an amniocentesis is required for confirmation. For more information see our pregnancy resources. None of the people we interviewed had had this test.
Last reviewed July 2017.
Last updated July 2017.