Complete guide to antenatal scans

What is an ultrasound scan and what scans can you expect to have during pregnancy?

Antenatal scans are only one part of your regular antenatal checks but they’re usually the part that’s most enjoyable and rewarding for prospective parents, giving them a chance to see their developing baby in the womb. Most pregnant women in the UK can expect to have only two scans, one at around 12 weeks and the other at around 20 weeks, but there may be reasons for having special, or extra, scans at other times throughout pregnancy, particularly if there are pregnancy complications or the pregnancy is multiple (eg. twins).


What is an ultrasound scan?
An ultrasound scan is a completely non-invasive means of assessing the growth and health of your baby in the womb and has a long record of successful use proving its safety. The scanning device or probe emits high-frequency sound waves which bounce off any solid objects they come across and travel back to the probe. The scanner then uses the different speeds with which the soundwaves echo back to the probe to calculate how far they have travelled, and so trace the outlines of your uterus, embryo/fetus and surrounding organs.

Scans available on the NHS are usually two- or three-dimensional, with three-dimensional scans giving a clearer picture of how your baby is developing. Four-dimensional scans are also now available privately and can allow for greater accuracy in looking for certain anomalies, as well as giving a fascinating view of how a baby moves in the womb.

In the UK, ante-natal scans are most commonly external scans, where the scanner is run over your tummy. Some antenatal scans, such as early dating scans, may use internal scans for greater accuracy.

What routine scans can you expect to have, and when?

  • The 12-week scan
    For most women in the UK, the 12-week scan is the first opportunity expectant parents have to confirm their pregnancy with images of their growing fetus. It’s perfectly normal for this scan to be scheduled between 10 and 14 weeks, depending on demand in your area. The purpose of this scan is to make sure that your baby is developing healthily so far, to check for multiple pregnancies and to confirm your due date. Many parents-to-be prefer to wait until after they have seen their baby on the 12-week scan before letting it be known that they are pregnant, as the chances of a miscarriage drop significantly once a healthy fetus has been seen.

In some areas you may be offered an earlier scan to confirm your pregnancy and to check for a heartbeat and implantation in the womb (see below).

  • The 20-week or ‘fetal anomaly’ scan
    The 20-week scan also has a window of a few weeks, though it’s not usually taken much before 20 weeks. This scan takes several measurements of the fetus to double-check the accuracy of your due date and also looks for any signs of developmental abnormalities, such as spina bifida. The scan can check the growth and performance of various organs including the baby’s individual heart chambers, lungs and brain, it also looks at the baby’s skeleton and the health of the placenta.

Girl or boy?
At the 20-week scan you may be able to find out the gender of your baby, if you are interested. Nowadays it’s quite common for expectant parents to want to find out whether it’s a boy or girl, so if you don’t want to know then make sure that you tell the sonographer your wishes, just in case.

Some hospitals have a blanket rule that they don’t tell the parents what the gender of the baby is. Ask ahead if this is something important to you.

Even if you do want to know the sex of your baby, there’s no guarantee that you’ll be able to find out as your baby’s positioning may prevent the sonographer from seeing the sex organs. Sometimes a sonographer may only see enough to make a tentative guess, and bear in mind that even the most emphatic verdicts aren’t completely reliable.

Further scans

  • Early dating scans
    In some areas you may be offered an early dating scan, around weeks six to eight. This scan checks for a heartbeat, location of the embryo and can quite accurately date conception. This scan is most likely to be offered if there has been some indication of a problem with the pregnancy, such as vaginal bleeding or abdominal pain (which may indicate an ectopic pregnancy). It may also be offered if there is a history of early miscarriage or ectopic pregnancy or other gynaecological problems that may affect the pregnancy.
  • Nuchal translucency scan
    The nuchal translucency(or nuchal fold) scan can help assess the likelihood of your baby having Down’s Syndrome but is not routinely offered to women under 35 (whose babies are at lower risk of developing Downs). If you’re 35 or over, you may be offered this scan when you start your antenatal care, if not, and it’s a scan you’d like to take, then you can ask your doctor for the scan.

The scan measures the fluid at the back of the baby’s neck and the nasal bone’s development, indicators of the possibility of Down’s. It is less invasive than a blood test and amniocentisis and carries no risk of miscarrriage (where amnio does). This scan needs to be performed during the first half of a pregnancy and may be offered alongside the 12-week scan (or you may need a separate appointment). The nuchal fold scan can be carried out privately if you feel the need for it but your hospital or doctor do not.

  • Extra scans
    If you develop a complication with your pregnancy, or you have a multiple pregnancy, you may be offered further scans to check on the health or position of the fetus, or the position of the placenta. Some common reasons for additional scans include multiple pregnancies, the presence of fibroids, or if you suffer from fibroids and if placenta praevia has been diagnosed at the 20-week scan.

20-week fetus – 4-D Image courtesy of Babybond
Want to see a bigger pic?

  • 4-D scans
    These are currently seldom offered on the NHS, but are available privately and can offer an incredibly detailed view of your baby. What you will see exactly depends very much on how your baby moves, and if s/he’s awake. These scans can be used diagnostically or simply just to get a different view of your developing baby. Costs vary depending on how long your scan is and what kind of photo or DVD package you opt for. Basic packages usually start at around £150.

If you can’t stretch to a 4-D scan it’s well worth having a look on the net at some 4-D pictures and short videos such as the ones on our weekly developmental newsletters or on

What happens during an ultrasound?
External scans

When having an antenatal scan in the UK it’s most likely that you’ll have an external scan. You’ll be requested to drink plenty of water in the hour or so before the appointment so that you have as full a bladder as possible when the scan is done. It can be a little uncomfortable timing-wise, but the reason for the full bladder is that it moves the uterus higher and so gives a clearer image.

You’ll be asked to lie on a bed and allow the sonographer or radiographer to get to your bare bump, or abdomen in the pre-bump days. There’s no need to take clothes off, but it helps if you wear clothes that you can easily pull up and down to expose your tummy. The sonographer then applies a clear, mineral-oil based gel to your stomach – it’s usually quite cold! – so that there’s no air trapped between your skin and the probe, and the probe can move smoothly over your body. The image (usually black and white only) created by the soundwaves is sent to a screen for both you and the sonographer to see. The sonographer will usually help you pick out different parts of your baby as he or she moves around in the amniotic fluid.

The sonographer may print stills from the screen to keep with your notes, and you may be able to take a copy home also, though you often need to pay a small amount for the privilege.

When the sonographer has seen everything s/he needs, you’ll be given a paper towel to wipe off the gel and the scan is over. A summary of the scan’s findings will be included with your notes and can be discussed with your GP/midwife. If the scan reveals anything unusual, or any cause for concern, you will be advised about what to do next.


Internal scans
With an internal scan a probe (shaped like a large pen) is covered in a sanitary covering and then in a clear, mineral-oil based gel and inserted into the vagina. This may be slightly uncomfortable, mainly because it’s not very dignified, but it shouldn’t hurt. You’ll need to remove your knickers and usually asked to put your legs up in stirrups to allow the sonographer access to your vagina. You may be given a robe to wear, but if not you’ll find that wearing a skirt you can pull up helps to preserve a little of your dignity. This method of scanning does have its advantages: The probe lies close to the womb and gives a very accurate image, so there is no need for you to drink water beforehand.

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