Things you need to know about pregnancy scans

While it’s great seeing your little starlet make her screen debut, there are medical reasons for having a pregnancy scan. So what are they really looking for? And what happens if something’s detected. We have the lowdown…

So, it’s your first ultrasound scan. Your excitement’s bubbling as the sonographer (that’s the person sweeping a hand-held gizmo over your tummy) checks the images of your baby bobbing about on a black and white TV screen.

While it might just look like a broad bean floating in fuzz, your scans hold a wealth of information that’s vital to you and your baby’s health.

 Generally, most women in the UK are offered two scans: an early dating scan, and a later developmental scan. In some health trusts e.g. Scotland and Portsmouth, however, this can differ, so always check with your GP or midwife what you’re entitled to.

Setting The Date

Falling somewhere between 10 and 14 weeks, your first scan takes about 20 minutes and dates your pregnancy, giving you and your midwife a due date to work towards.

‘A crown/rump measurement from the top of her head to the end of her bottom helps us calculate how old she is,’ says sonographer Janette Keit. ‘We can also see whether you’re carrying twins or more.’

For most women the first scan is a time of celebration and typically you’ll leave hospital with a printed summary of your scan. However, for a few women the scan may sadly reveal baby has stopped developing.

‘An empty sac (blighted ovum) shows your baby didn’t grow, while an embryo with no heart beat reveals the pregnancy failed. Measuring your baby can indicate at what stage things went wrong,’ says Janette.

In these cases, a doctor will discuss your options - whether it’s letting nature take its course (eventually you’ll miscarry) or having an ERPC (Evacuation of Retained Products of Conception) under general anaesthetic.

‘I was grief stricken when my first scan showed my baby had no heartbeat. For me, having an ERPC gave me closure and put my periods back on track,’ says Jill Leader, 32, from Chester, mum to Dylan 14 months. ‘Six weeks later I was pregnant again and 10 weeks after that I was having another scan. The relief at seeing Dylan’s heartbeat was indescribable.’

Attention To Detail

An anomaly scan is typically done around 19 to 20 weeks to monitor your baby’s development. ‘By this stage everything is formed so we can have a detailed look to check for structural abnormalities,’ says Janette.  ‘We also take various measurements to check the baby’s growth.’ All of which should be noted in the printed report you’re given afterwards.

At this stage, about half of all major abnormalities, such as spina bifida or defects of the abdominal wall, can be identified. In other cases the scan may show minor changes, known as ‘markers’. These can be a sign of a more serious problem such as Down’s syndrome.

‘Markers may or may not indicate an underlying problem with the baby’s chromosomes,’ says Janette. ‘Further testing such as Chorionic Villus Sampling [a definitive diagnoistic test, drawing cells from the placenta, done at around 10 weeks] or amniocentesis [another definitive test, this time drawing cells from amniotic fluid, available from the fifteenth week]  is needed if you want definite answers.’

If the sonographer finds anything unusual you’ll see a doctor within 24 hours or, if necessary, a consultant fetal medicine specialist within 72 hours, for further tests. You’ll then need time to make some big decisions which may include ending your pregnancy, preparing for the birth of a baby who needs special care, or, very rarely, allowing surgery on your unborn baby.

The Antenatal Results and Choice charity (set up to provide support and information to parents throughout antenatal testing) can provide invaluable advice (www.arc-uk.org), but it’s reassuring to note that 95 out of 100 babies are born without abnormalities and the few who are don’t necessarily have problems that can’t be treated.

‘The sonographer will use this scan to check your placenta,’ says Janette. If it’s low-lying, it can lead to problems in late pregnancy, blocking your baby’s exit, or cause serious bleeding. In this case you’ll need a C-Section. However, although a third of placentas are low in early pregnancy, very few are at term.

‘I was gutted when the sonographer told me my placenta was low,’ says Rebecca Brown, 28, from Warwick, mum to Thomas, eight months. ‘I was convinced I’d need a caesarean. When I went back for another scan at 36 weeks, my placenta had moved up. Thomas was born naturally two weeks later.’

This scan can also reveal the sex of your baby, ‘but if he’s lying in a awkward position it may be difficult to tell,’ says Janette. Because of this, some hospitals won’t tell parents as they can’t be 100 per cent certain.

Scan Glossary

What those letters on your scan report mean:

CRL: Crown Rump Length
HC: Head Circumference
BPD (Biparietal diameter): Head diameter
AC: Abdominal circumference
FL:  Femur or thigh bone length

Testing Times

According to National Institute for Clinical Excellence (NICE – an independent organisation set up to provide national guidelines for good health and treating/preventing ill health) guidelines, the choice on whether to have routine screening tests is yours, but your GP or midwife should make you aware of what those decisions mean for you and baby. If you do opt for scanning, those you have out of choice, rather than for medical reasons (see below), must be paid for.

Early Scans

If you’ve previously miscarried, or you bleed in the first few weeks of pregnancy, you may be offered an early scan (6-10 weeks) to confirm your pregnancy, or rule out an ectopic pregnancy. This may be done vaginally to give a clearer picture of the tiny baby.

Later Scans

Checking growth: If your baby doesn’t grow at the expected rate, a Doppler scan (which measures blood flow) can detect placental problems and predict your risk of pre-eclampsia. Growth scans may also be recommended if you’re having twins or your baby is larger than expected.

Checking position: If your midwife thinks your baby is breech at 37 weeks, a scan will confirm this. Scanning assesses your baby’s size and exactly how she’s lying so your doctor can decide on the safest way to deliver.

Checking bleeding: Bleeding is common in the third trimester and while a scan rarely reveals the cause, it can reassure you that your baby’s fine.

Nuchal translucency test: As the most accurate screening (i.e. not diagnostic) test for Down’s Syndrome, this uses ultrasound to measure the fluid between layers of skin behind your baby’s neck. Those with Down’s have more fluid than those who don’t. 

The measurement is fed into a computer with your age, your baby’s heart rate and any blood test results, giving you a risk factor. If you’re high risk you must decide whether to have further definitive tests, like CVS or an amniocentesis. Only seven per cent of women are offered a nuchal scan on the NHS but it’s available privately from £90 to £150.

4D Scans: 4D scans offer a more solid, life-like picture of your baby than the conventional 2D scan. They cost around £200 and are best between 26 and 32 weeks.

Reader panellist Michelle Hill, 33, is mum to Liberty, nine, Hope, one, and is 37 weeks pregnant

‘When my baby was measured she was two and a half centimetres smaller than she should have been so I’ve had a scan once a week from 35 weeks to make sure that she’s growing properly.

Thankfully, although she’s small, she’s been developing at a normal rate. If she stops growing properly I may have to be induced which would be a shame, as I wouldn’t be able to have the home birth I want. As long as she’s healthy, though, that’s all that matters.’

Reader panellist Louise Freeborn, 28, is 31 weeks pregnant with her first baby


‘I’ve had to have quite a few extra scans because I was born with a hole in my heart and a leaking valve. My sister has a heart problem too so my consultant is concerned the heart condition might run in the family. Luckily, so far the scans have shown that everything’s fine.’