Tests during pregnancy: what should you have?

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  • Many pregnant women want to take full advantage of the various tests and scans on offer to check that their baby is healthy.

    So what exactly are these tests, and what happens if the results aren’t what you’d hoped for?

    Worrying about the health and development of your unborn baby is normal and is likely to continue until the day you give birth. But whereas once everything was left in the hands of fate, nowadays there are seemingly countless tests on offer that will monitor your baby’s development and flag up any serious concerns. So, what does each test look for, how is it performed and what do the results tell you?

    Your options

    The fact remains that you don’t have to have any tests or scans at all throughout your pregnancy if you don’t want to. When you attend your first antenatal appointment, you’ll be handed leaflets explaining what each one is and, if you want, you’ll usually get booked in for your nuchal or dating scans and may be given a date for your 20-week anomaly scan.

    Not surprisingly, at the point when the pregnancy is still a little surreal, it’s tempting to slip into autopilot as you head off for your scans or blood tests and not think about what they’re looking for until you’re actually confronted with a possible problem.

    Tests can be extremely reassuring, but bear in mind they can also cause needless worry and anxiety. So although your chances of having a healthy baby have never been better, it’s worth thinking about, and discussing with your partner, if you have one, what you would want to do if there was a problem.

    There are two types of tests available: screening and diagnostic. Diagnostic tests, such as amniocentesis and chorionic villus sampling (CVS), give a 99.9% reliable answer if there is a defect. Screening tests, such as blood tests and ultrasounds, simply look for signs of possible abnormalities and give you a ‘higher or lower than average’ risk assessment.

    Screening tests

    Dating scan

    This ultrasound scan, which helps decipher your due date, is routinely offered to all women between 8 and 12 weeks. The dating scan can also pick up serious problems such as if the baby’s heart has stopped beating, or the brain, internal organs or limbs haven’t formed properly.

    You lie on a bed and the sonographer spreads a jelly-like substance on your bump to help the hand-held transducer (which looks a bit like a computer mouse) move across your tummy. This produces a picture of your baby on a computer screen, which then allows the sonographer to look in detail at the baby and take measurements.

    If a scan’s needed before 8 weeks, perhaps because of a previous miscarriage, to confirm a pregnancy, or if an ectopic pregnancy is suspected (where the baby develops in the Fallopian tubes), it’s done using a thin probe, which is inserted into the vagina. This gives a clearer picture of the baby in early pregnancy, but it may feel a bit uncomfortable.

    Nuchal scan

    In some parts of the UK, mums-to-be can have a nuchal scan at the same time as their dating scan, which uses ultrasound to assess the risk of Down’s syndrome and other chromosomal problems by measuring a gap at the baby’s neck.

    The measurement, together with your age, is calculated to give a risk factor. If your result represents a higher chance than one in 250, you’ll be offered a CVS or amniocentesis, and counselling about what these options entail. You’ll be told there and then if there’s a potential problem and not just be sent away without an answer. The advantage of a nuchal scan is that its timing allows for action to be taken while the pregnancy’s still in its early stages.

    Nuchal scans are mainly available in London and the south-east. Some centres offer them privately (look for a centre accredited by the Fetal Medicine Association; www.fetalmedicine.com) at a cost of around £150.

    Anomaly scan

    If you choose to have an anomaly scan, which is standard on the NHS, you’ll be booked in to have it at around 18 to 22 weeks.

    Using ultrasound, the sonographer will take a very detailed look at your baby, the amount of fluid surrounding it and the position of the placenta. She’ll check the baby’s growth and development, and can pick up conditions such as spina bifida or problems with the limbs, heart, kidneys, liver, bladder, lungs and brain.

    If a problem is suspected, it may simply require extra monitoring and may remedy itself.

    A detailed cardiac scan can give a clearer picture if a heart problem is suspected, while a Doppler scan might be recommended if your baby’s measurements are on the small side, to check the flow of blood and nutrients through the placenta. Both of these are non-invasive and are done using ultrasound. At this stage in your pregnancy, an amnio is the only option to give a ‘yes’ or ‘no’ answer if a scan shows a risk of Down’s syndrome or other chromosomal syndromes.

    3-D scans

    These give a fully rounded picture of your baby and are popular for bonding purposes, as you can get a real idea of his/her facial features. They’re not generally offered on the NHS unless a facial defect, such as a cleft palate, is being checked out. Private centres charge around £200-£300 for a 3-D scan.

    Group B Strep test

    This is probably the least common test, but just as important. Group B Strep (GBS) is a bacterial infection that can affect a baby around labour and birth and potentially cause problems.

    The test works using something called an enriched culture method (ECM). If you want it done, get your doctor or midwife to order the test. There are some NHS hospitals that do the test, but you’ll probably have to pay to get it done privately.

    The GBS Screening Pack is sent out by post and involves two swabs, one vaginal and one rectal. These should be taken between 35-37 weeks of pregnancy – you can do them yourself or ask your doctor or midwife to do it. The swabs are then sent straight to the testing lab in packaging that comes as part of the GBS Screening Pack. If you don’t get it on the NHS, the test is usually free but you will have to pay to get the results analysed – usually around £30. For more information about the GBS test, visit the Group B Strep Support website

    Blood tests

    Hospitals around the country use different types of blood tests to screen for Down’s syndrome and neural tube defects.

    A blood sample will be taken from you at around 15 to 19 weeks, after which the naturally occurring pregnancy hormones in the blood are analysed. Taking into account your age, the levels are compared to a chart showing normal levels for that stage of pregnancy. A computer will calculate whether you have a high or low risk of having a problem compared to the norm.

    Results take between 7 and 10 days and will tell you whether you’re screen negative, which means your risk of having an affected baby is less than one in 250, or screen positive, where the risk is more than one in 250. But unreliable results, giving what’s called a false positive, can be caused by various factors – for instance, if a woman is very underweight or overweight, if she’s had recent vaginal bleeding or is less or more pregnant than she realised.

    Similarly, blood tests may fail to pick up problems and can give a false negative result. The reliability of results varies from hospital to hospital, so ask your doctor what the false positive rate is where you have your test.

    If a test comes back ‘high risk’ (which is the way some hospitals describe a result higher than one in 250), couples face the difficult decision of whether to have an invasive test, which runs a small miscarriage risk, to find out for sure. If you’re faced with this decision, ask for counselling or call Antenatal Results and Choices for advice.

    Diagnostic tests

    Chorionic villus sampling (CVS)

    CVS is used to detect Down’s syndrome and other chromosomal disorders, and can be performed earlier in pregnancy than an amniocentesis test – from about 11 weeks. Like an amnio, it’s an invasive test and involves taking a tiny amount of tissue from the placenta by passing a thin needle through the stomach wall, or inserting a small tube through the vagina and neck of the womb.

    Some women describe it as uncomfortable but not painful and some hospitals offer a local anaesthetic. Ultrasound is used as a guide, and the procedure takes around 20 minutes. The placenta contains the same DNA as the baby, so it accurately detects major chromosomal problems. You’ll get results within 10 to 14 days.


    Amniocentesis is also an invasive test, but instead of taking tissue from the placenta, about two tablespoons of amniotic fluid from around the baby are removed and analysed. It can be done at, or after, 15 weeks (which is too late for CVS) and will be offered to mothers if a screening test flags up a higher-than-average risk of Down’s syndrome; when a previous pregnancy has been affected by a chromosomal or genetic disorder; if a scan has shown up markers for Down’s: or if there’s a family history of chromosomal abnormalities.

    The procedure is usually quick, although it may take 20 minutes or so to locate a pocket of fluid away from the baby or placenta. The process may also cause a little discomfort to the mum-to-be.

    Ultrasound guides the doctor as she inserts a fine needle through the woman’s stomach wall into the amniotic fluid to take the sample. A result for Down’s syndrome, Edward’s syndrome and Patau’s syndrome may be available within three days, and results after looking at all the baby’s chromosomes within two or three weeks.

    If a CVS or amniocentesis result shows that there is a disability, depending on the nature and extent of the problem, you may be offered a termination of pregnancy. You may want to ask for information on what the baby’s condition involves and how her life expectancy and quality of life will be affected.

    Termination is a very personal decision and although hospital counsellors, doctors and self-help bodies, such as the ARC, can offer support and advice, only you and your partner can decide if it’s the right thing for you.

    What’s the risk for my baby?

    Generally speaking, ultrasound scans are considered safe for both mum and baby, although no one can say categorically that they are 100% risk-free.

    With CVS, there’s a 1-2% chance that you’ll miscarry, which is higher than the miscarriage rate for amniocentesis (currently around 1%). One explanation for this is that it’s performed before 12 weeks, when more miscarriages would happen anyway.

    You can ask at your hospital what their rate is. A skilled practitioner helps reduce the risk, so check that the person who will perform the procedure is doing at least one a week. For more info, call the Antenatal Results and Choices (ARC) helpline on 020 7631 0285.

    Things to consider beforehand

    *How will you take the results if a serious problem is suspected?
    *Do you think you’d terminate the pregnancy if there was a problem?
    *Would you like to know if there’s a problem in order to prepare for it, even if you wouldn’t terminate?
    *How will you feel if the result of a scan is inconclusive and an invasive test is the only way to be sure if there’s a problem?
    *Do you have the right support around you? Have you talked it all through with your partner or a friend?
    *Are you having these tests because you want to, or because you feel you should?

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