Antenatal Screening

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'). 

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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.

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.

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.

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.

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.

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.

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.


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