20 week anomaly scan: here’s what to expect

What happens at your 2nd NHS ultrasound scan? What does it check for? And will you find out if your baby's a boy or a girl?

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Your mid-pregnancy ‘anomaly’ ultrasound scan is your 2nd routine NHS pregnancy scan. It usually happens at about 20 weeks into your pregnancy, and takes a really detailed look at your baby and your womb.

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It’s basically a scan to check whether your baby is developing normally, and whether there are any physical abnormalities (or anomalies).

“We get a really clear picture of your baby’s anatomy from this scan,” says Nigel Thomson, Professional Officer for Ultrasound at the Society and College of Radiographers. And, because there’s so much detail to see, says Nigel, “the resulting pictures you can take home can be truly stunning!”

You may also get the chance to find out – if you want to – whether you’re expecting a boy or a girl.

What exactly does the scan check for?

This scan looks in detail at your baby’s:

  • Spine
  • Head
  • Face
  • Heart
  • Abdominal wall 
  • Stomach
  • Kidneys
  • Arms and legs
  • Hands and feet

And there’ll be a check of your placenta, too, to see where it’s lying and make sure it’s developing as it should.

The sonographer who’s doing your scan will look specifically for signs of 11 conditions, including cleft lip, spina bifida and serious heart abnormalities. All of these conditions are uncommon – and some of them are very rare – so, for most women, this scan will show that your baby seems to be developing quite normally.

Do I have to have it?

No, not if you don’t want to. It’s completely up to you.

Will I have the scan at exactly 20 weeks?

Not necessarily. Most anomaly scans are scheduled for sometime between 18 and 21 weeks and, in some areas it may be carried out later than 21 weeks. 

What do I need to do beforehand?

As with your 12-week scan, you’ll probably be asked to arrive with a full bladder (as this can push your uterus closer to the surface, and help the sonographer pick up a better scan image.)

You might want to bring someone with you to share the experience – your partner or another family member, maybe. But it’s entirely up to you. 

If you already have children and want to bring them with you, though, it’s worth checking with the hospital that this is OK: quite a few ultrasound departments don’t allow children (largely because this scan requires a lot of concentration from the sonographer)

However, if children are allowed, it can be lovely experience, as Smilerkinners, who posts in our MFM Chat forum, found out: “Kiddies loved seeing ‘baby sprout’… It’s been an exciting day for all!”

woman having scan

What happens at the scan? 

The procedure will be the same as it was for your 12-week scan: dimly lit room, (cold) gel on your bump, and then a slight pressure as the sonographer passes a handheld transducer over the skin of your belly.  

The next thing is the black-and-white image of your baby appearing on the sonographer’s screen. Often, you can see all, or part, of the screen too, or it’ll be turned towards you after a few moments.

This is when your sonographer will really have to concentrate hard. “They have to look really carefully at your baby from top to toe,” says Jane Fisher from the antenatal-testing support charity Antenatal Results and Choices (ARC). “And there a lots of measurements that need to be taken.”

This means it may be a little while before your sonographer can talk you through what’s showing on the screen. So don’t panic if there’s silence for a bit!

“Don’t be alarmed if they spend a lot of time doing checks, ” says MFM forum mum LH86. “[This time round], the sonographer spent at least 10 minutes just looking at the heart, slowing it down, rewinding it, speeding it up and flipping it over and around. We were starting to panic that she was going to tell us something was wrong but she said she was just counting the blood vessels and stuff.”

How long does it take? This scan will probably take longer than your 12-week one, so do expect to be in there for about half an hour.

“This is a very comprehensive scan and there is a lot of work for the sonographer to do,” says Nigel. “You can expect to be in there for anything up to 30 minutes.”


20 week scan showing baby waving arm

Will the picture be clearer than last time? Will I be able to see my baby’s face?

Yes, there’s usually a lot more to see this time round. But the amount of detail does vary hugely from person to person. “It depends which way your baby is lying, and how much movement he or she is making at that particular time,” says Nigel. “And also if you have a high BMI (body mass index), it can mean that it’s harder sometimes is to see.”

All things being well, though, you should see much more of your baby than you did at your 12-week scan, including closer-up shots of arms and the face. And, if your baby’s moving, you may even see some wriggles or kicks, like MFM forum regular Queen Asanti 83: “My scan went really well today. Everything’s looking fine. We saw our baby yawning and it gave us a little wave!”

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Will I definitely find out the sex of my baby?

Yes, your sonographer will (almost) certainly tell you if you’re expecting a boy of a girl – if you’d like to know.

MFM forum user BellesMommy7 definitely did want to know. “I had my 20 week scan yesterday, and it was truly amazing! At the beginning, we were asked if we wanted to know the sex and we agreed we did, but we asked to be told in code, as our gorgeous 4-year-old daughter was with us. As I watched the lady write down the answer to the said question, I was convinced she wrote ‘girl’ but [when I looked at the paper, she’d written] ‘boy’!”

However, it’s worth knowing there are some hospitals who tell you the sex of your baby, even if you ask – in case a mistake is made. That’s because spotting whether it’s a girl or a boy is not an exact science (and babies sometimes go all shy and cross their legs at the crucial moment).

“It should be stressed that this is not officially part of the screening program,” says Nigel. “Most sonographers are happy to give an opinion, if that is what you would like, but you should check with your hospital or midwife as to the policy of your trust.”

If you do get the boy/girl opinion, Nigel reckons there’s over a 95% chance it’ll be right – but there is no guarantee, as some of our MFM mums have found out.  

And if you don’t want to find out, don’t panic if, like MFM mum Danipeter, you see the word ‘female’ printed out on the top of your scan photos. That’s you it’s referring to, not your baby! 

As Cupcake mummy explains, “The ultrasound machines/computers used for scanning aren’t just used in antenatal care, and sonographers input the settings as required – including the sex [of the patient they’re scanning.”

Phew!

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Will I get results – and the photos – straightaway?

Yes. 

If the scan result’s OK, does it definitely mean there’s nothing wrong with my baby?

Very probably. But, as the scan only looks for certain specific problems (and there are some other conditions that might not show up until much later in your pregnancy), it cannot absolutely find everything that might be wrong.

Before you go home, you may get issued, along with your scan photos, a ‘scan report’ with lots of measurements on it.

MFM forum user ilovemygirls got a little concerned when she had a look at hers: “I’m a little worried as [it says] her head was measuring ‘small’ at 162.7mm.”

But as fellow MFM mum MrsW2012 says, “A friend of mine is a midwife. She says not to worry as it is guidance only and if there were any concerns, they would have been mentioned at the scan. If you aren’t sure, I would call your midwife and ask.”

And if the result’s not OK, what then?

If there’s an issue with your scan, it’s usually for 1 of the following reasons:

  • The sonographer couldn’t see everything she needed to. This doesn’t necessarily mean there is a problem. As MFM forum mum supersquish recalls: “My scan went well but I have to go back so she could check the heart chambers as the baby’s spine was blocking her view – but she said all is well as far as she can see.”
  • Your baby seems to be measuring ‘small for dates’. This could be an indication of problems with your baby or with your placenta. Or it could just be that your baby is perfectly healthy but currently a little smaller than expected.
    This was the case for MFM mum icsibaby: “My 20-week scan showed my baby was on the 2nd centile. I had 3 further growth scans which all said she was on the lower end of the scale but nothing to worry about. I had her on my due date and she absolutely fine – 5lb 5oz, so dinky in relation to most but perfect in every way!”
    If your baby measures ‘small for dates’, you may be offered further tests or further scans, like icsibaby, maybe with a fetal medicine specialist. You’ll be given plenty of information about any follow-up tests and scans that are suggested, and you’ll be able to discuss the best next steps with your midwife or consultant.
  • Your sonographer has seen a specific problem. This could be:
    • A ‘soft marker’. “This can sometimes indicate that there is a problem with your baby’s chromosomes, which could indicate Down’s syndrome, for example,” says ARC’s Jane Fisher. “Depending on the type and number of soft markers, you may be offered an amniocentesis to rule out chromosomal problems.”
    • A untreatable condition that may, unfortunately, mean your baby can’t survive. 
    • A treatable condition – which means your baby will need surgery or treatment when he or she is born, or maybe even in the womb.

Again, you’ll be given plenty of information and support and the opportunity to discuss the best next steps with your midwife or consultant. You may also want to call the trained staff on the ARC helpline (Monday to Friday, 10am to 5.30pm) on 0845 077 2290 (or 0207 713 7486 from a mobile.)

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