What to expect from your 20-week pregnancy scan

20 week scan

The 20-week scan is also known as the mid-pregnancy ultrasound or the anomaly scan. It is usually done between 18 weeks and 20 weeks plus six days gestation, however some hospitals do it later. The sonographer will be looking for any abnormalities in your baby's development, and you may be able to find out the baby's sex.

What happens at the 20-week scan?

It's exactly the same format as the 12-week scan so it's the same drill for you: full bladder before the scan, gel on belly, picture of baby on screen. This scan may take a bit longer, however, as the sonographer will have a really detailed look at the development of your baby, and the health and position of your placenta.

You might not experience quite the same “wow” moment with this scan as you did when you saw your baby for the first time at the end of your first trimester. By the 20-week scan you'll be an old-hand at this lark, after all, and may even be feeling your baby's movements already. This will probably have reassured you and so you're not likely to have the same “there really is a baby in there” moment.

But the image you'll see of your baby is much more detailed than at your 12-week scan, and it can be a mind-blowing experience, with you getting to see some really amazing close-ups of your baby in the womb.

To give you a taste of what lies ahead – ie babies don't always do what you want them to – how much the scan shows may be affected by your baby's position at the time of the scan.

How long does the mid-pregnancy scan take?

I definitely felt nervous at my 20-week scan even though 12 weeks was absolutely fine. I think it's perfectly normal to be nervous.

Usually about half an hour, but if your baby is in a tricky position it may take a little longer. It can feel as though the sonographer goes silent for ages – don't panic if this happens. They're doing lots of measurements and calculations. It's perfectly normal for them to take their time doing this and not say anything for a while.

Can I take my partner or a friend to the anomaly scan?

Yes, it's usually fine to take someone with you. Do be aware that this scan in particular is to look for potential problems (and isn't just a high-tech gender reveal party!) and if you are one of the unlucky ones, it can be quite upsetting, so you might want to consider this before bringing along any older children you have.

Will I find out the sex of my baby at the 20-week scan?

20 week scan

You might well do. And on that note, if you don't want to know, for goodness' sake tell the sonographer at the start of the scan. You'd be surprised how many women think the scan won’t give away anything and are immediately greeted by an enormous willy swinging in the breeze.

On the other hand, some hospitals have a policy of not telling parents the sex of their baby, so it's worth checking beforehand so you aren’t disappointed on the day.

Will I get a picture of my baby from the 20-week ultrasound?

Most hospitals will give or sell you a photo to take home. Remember that the paper they are printed on is heat-sensitive so, tempting though it is, don't laminate it or it will vanish!

What does the 20-week scan show?

The anomaly scan checks your baby for structural abnormalities. The sonographer will check your baby's head, face, spine and see whether all the bones align.

All internal organs will be checked to see that they have developed properly. The heart is looked at very closely to ensure the four chambers are of equal size and the valves appear to be working with every heartbeat.

Your baby's kidneys and stomach will be looked at to see if they're functioning properly, and limbs, hands and feet will also be examined.

The position of the placenta will be noted; if it is lying low in your uterus you will need to have another scan later on. A low-lying placenta usually moves up by the third trimester.

The sonographer will also check the umbilical cord is working properly and that the volume of amniotic fluid surrounding your baby is at the right sort of level.

Prepare for a near silent scan, as the technician will be concentrating – this is not necessarily a bad sign.

There will be various measurements made during the anomaly scan:

  • Head circumference
  • Abdominal circumference
  • Thigh bone (femur) length

These measurements indicate whether your baby is developing as expected and can help confirm that they have your estimated due date correct.

When will I get the results of the 20-week scan?

Immediately. They will tell you then and there if there are any potential problems or not and whether your baby seems to be growing well.

What problems might be found on the anomaly scan?

As well as developmental checks, the sonographer is looking for specific conditions, some of which may be treatable, while others could sadly jeopardise your baby's survival.

These are the 11 conditions that are being looked for during the anomlay scan (the varying detection rates are as documented by the NHS Fetal Anomaly Screening Programme):

  • Anencephaly (a brain disorder) 98%
  • Spina bifida 90%
  • Cleft lip 75%
  • Serious cardiac abnormalities 50%
  • Bilateral renal agenesis (where the kidneys fail to develop) 84%
  • Lethal skeletal dysplasia (where the skeleton does not develop as it should) 60%
  • Edwards' syndrome (Trisomy 18) 95%
  • Patau's syndrome (Trisomy 13) 95%

Abdominal defects:

  • Diaphragmatic hernia 60%
  • Gastroschisis 98%
  • Exomphalos 80%

It's important to remember that the vast majority of women come out of the 20-week scan having found no problems at all and feeling reassured, so try not to work yourself up into a panic about it beforehand.

What happens next if they find a problem at my 20-week scan?

If the sonographer detects any problems, they will probably ask for someone to come and have a look to give a second opinion. If they think there could be an abnormality you will be referred to a fetal medicine specialist and should be seen within a few days. You may be offered amniocentesis or other diagnostic tests as well.

At the fetal medicine unit you will be examined again to ascertain more about what the issue is and what can be done. What happens next depends on what the problem is and how serious it is.

It may be that your baby can be treated within the womb or that they will need treatment or surgery after their birth, possibly immediately, so this will all be set up in advance of your due date.

Sadly, in a few instances, you may be given the option to end your pregnancy. You will be given counselling and support when making this tremendously difficult decision. If you need to discuss your scan results, head to our Antenatal tests and choices Talk forum.

Do I have to have the anomaly scan?

No, it's entirely up to you. Some women do choose not to go ahead with it because they know that the results wouldn't mean they did anything differently and they therefore prefer not to have the scan in the first place.