6 minute read
FOCUS ON: SCANS
Dr Chiara Hunt AND Marina Fogle DISCUSS THE VARIOUS SCAN OPTIONS AVAILABLE THROUGHOUT YOUR PREGNANCY
Seeing your baby at any of your scans is an unforgettable moment. During your pregnancy, you’ll have two main scans: the 12-week check-up and the 20-week scan – both performed using ultrasound. Ultrasound scans have been used in pregnancy since the mid-1950s and have no known side e ects for mother and baby. They’re a really good way of having a non-invasive yet detailed look inside the uterus at the developing fetus.
It’s now widely accepted that due dates predicted from scans are the most accurate. Of course, if you’ve had IVF and know the precise date of implantation, you will know exactly. If you believe you know because ‘it could only have happened on one night’, remember that sperm can live for up to seven days, so fertilisation can occur on the day you have sex (if you happen to ovulate that day) or a few days later. It’s fairly common for your due date to be recalculated after your scan, and it might have changed by up to a week or so. The scan date is more accurate, but do bear in mind that your baby is likely to arrive anywhere between three weeks before and two weeks after that date.
It’s important to remember that, although the scans are good, they don’t always detect every abnormality. A normal scan, although reassuring, doesn’t give a 100 per cent clean bill of health. For example, of the one per cent of babies born with a heart abnormality, about half of these are picked up at birth or later. The scans only look at the structure of the organs; they can’t give us much information about their function; this can be more carefully assessed after the baby is born. Although for many this is a happy experience, for an unlucky few the 12-week scan is when they’ll find out they’ve had a miscarriage, so it’s normal to feel both nervous and excited. And while you may have to follow new Covid-19 guidelines, you can be rest assured that you will have all your necessary scans.
THE 12-WEEK CHECK-UP (NUCHAL SCAN)
The 12-week check-up is really important. Using a combination of ultrasound and a blood test, it determines the risk of the fetus having a chromosomal abnormality, such as Down’s Syndrome, as well as many other things, including genetic syndromes and structural abnormalities. The ultrasound scan checks the fetus is growing well, but another purpose is to look at the translucent, or clear, space in the tissue at the back of your fetus’s neck – hence, the name ‘nuchal scan’. The baby’s nasal bone is also measured. Babies with abnormalities tend to accumulate more fluid behind the neck and have absent nasal bones. Sometimes this scan is also called the ‘dating scan’, as it accurately predicts the due date more so than dating from your last period.
In order for the tests to be accurate, the check-up must be done between 11 and 14 weeks. It doesn’t give you a diagnosis of any abnormalities, simply an idea of whether you are at high or low risk of certain conditions. If the risk is deemed high, you may be advised to have chorionic villus sampling (CVS) or amniocentesis tests; these are the only EXTRA SCANS There are many other scans and tests available privately. Here are your options:
• Fetal viability scans, at six to 10 weeks, will check that the embryo has implanted correctly and, from seven weeks, you’ll be able to hear a heartbeat. This scan is often done internally. Cost: approx £100. • 3D scans show still images of your baby in three dimensions. 4D scans show moving 3D images of your baby. Parents will see baby’s skin, rather than her insides. You may also be able to see the shape of your baby’s mouth and nose.
The best time to have either of these is between 26-30 weeks. Cost: from £50. • There’s mounting pressure for late scans to be included routinely in NHS care, but currently, unless there are problems, y fin l n ld e t ee A late scan will check that the baby is growing nicely and that the placenta looks healthy and is working properly and will measure the amount of amniotic id t i t l d le n t e t e l d in t e umbilical cord. Cost: approx £150.
accurate ways of testing for chromosomal abnormalities. However, they are invasive and associated with a small risk of miscarriage. Bear in mind that CVS isn’t usually done after 14 weeks, so it’s a good idea to have the 12-week scan sooner rather than later, allowing time to arrange further tests if necessary.
NON-INVASIVE PRENATAL TESTING (THE HARMONY TEST)
Fairly recently, a new test has become available in the UK, known as non-invasive prenatal testing (NIPT). This is o ered in private clinics under brand names such as the widely known Harmony Test, as well as Nifty, Panorama, Verify, MaterniT21 and SAFE. The NHS has started using it, and an increasing number of trusts o er it to women deemed high-risk after the initial combined screening, instead of proceeding straight to invasive testing, such as amniocentesis and CVS, which carry a chance of miscarriage, while NIPT doesn’t.
The NIPT test works by detecting the baby’s DNA in the mother’s blood from a simple blood test, usually taken at around 10 weeks. By detecting this DNA, the lab can much more accurately (around 99 per cent) assess the risk of genetic abnormalities, such as Down’s Syndrome. Currently in the private sector, this type of test costs around £500. If the test is positive, the result would still need to be confirmed with amniocentesis or CVS.
Most professionals agree that NIPT is an exciting medical development, which in future may prevent the miscarriage of healthy fetuses through invasive DNA testing. We all know that the NHS is stretched financially, so cannot always o er the newest tests immediately. Therefore, for those mothers who have a history of genetic abnormalities or are slightly older – and therefore at an increased risk – and can a ord it, NIPT is worth doing.
THE 20-WEEK SCAN (ANOMALY SCAN)
For most women, the 12-week scan is the green light to celebrate and get excited about being pregnant. But eight weeks later you have another ultrasound that looks closely at how the fetus and all her organs are developing. Rather than just a quick look to see if all is well, or simply to tell you the sex of your fetus, at the 20-week scan the sonographer will spend a lot of time looking at your fetus’s various organs to check that they’re developing as they should be.
What will be checked?
• Head and brain • Heart – its chambers, valves and blood vessels • Abdominal contents – particularly the kidneys and stomach • Spine • Facial features • Hands and feet • Placenta, umbilical cord and amniotic fluid • Genitals – this is usually when they can let you know whether you’re having a girl or a boy. Unfortunately, it’s at this scan that abnormalities are sometimes found. Most irregular findings are minor and may require rescanning or surgery, but will not necessarily a ect the outcome of your pregnancy. But in some cases, the abnormalities are potentially life-threatening. This is devastating for parents, but the teams are specially trained to support couples at this time and o er excellent care.
Do remember that these cases are very rare indeed. In the UK, we’re lucky to be at the cutting-edge of science, and every precaution is taken to ensure that our babies arrive in our arms fit and healthy. For most mothers, the 20-week scan is an amazing window to their uterus, where they can see their perfect little baby growing beautifully. So, enjoy it and be prepared to get emotional!
