Can an Ultrasound Miss Twins?

Can an ultrasound miss twins, and how does it happen?

Can an Ultrasound Miss Twins

When one of my friends was going for her 8 week scan, she was desperately excited.

'It's twins!' she would say to anyone who would listen. 'I know I'm having twins. I can feel it!'

But when she got back and everyone asked her if her suspicions were true, she seemed almost disappointed when she said she was only having one child.

Of course, she was still amazingly happy that her baby was healthy, and felt incredibly blessed to be having her child.

Of course, when she went in for her first scan in her second trimester and it turns out that she was having twins, it made the surprise all the sweeter!

What Goes on When You Have an Ultrasound Scan?

Ultrasound scans are harmless regular procedures that you have to check on your baby, and make sure that everything is progressing like it should.

It can be external (the one you see on television), where the medical examiner uses a handheld device that produces high frequency sound waves, way beyond the limit of human hearing, then picks up on the reflections of these sound waves to create a picture of what's going on inside your body.

You can also have internal scans, where a tiny little probe is inserted into your body so the doctors can get a more detailed picture of certain areas. This is less common, but just as safe and nothing to worry about.

Not all women have ultrasound scans in the first trimester, and if you do, it will generally be just a simple check to determine the age of your fetus. It's the second trimester ultrasounds, normally performed between your 18th and 22nd week, that are more detailed, and used to check for fetal heartbeat and breathing, your child's movement and size, gender, peculiarities with amniotic fluid and placenta, and if there's any problems.

So Can an Ultrasound Miss Twins?

It can, but it's pretty unlikely, especially with the second set of scans. Advances in ultrasound technology and the rise in the amount of twins being conceived mean that the medical professional performing your scan is far more likely to be familiar with the signs of twins.

If your scans miss twins, it will generally be the early scans, and bear in mind it's still really unlikely that they're going be missed.

You've also got to consider that there's a large amount of signs that you're going to have twins. You might have some of these signs already, or you might just have a strong feeling that you're going to have twins.

If you do have a strong feeling that you're having twins, and a scan only shows one, it's not cause for alarm.

If It's Really Unlikely, Then How Can Twins Hide on Ultrasound?

Sometimes, especially early on, your twins might be doing what's called 'shadowing' each other. What this means is that one is sitting behind the other, which can lead to twins not seen on ultrasound scans. Because an ultrasound essentially makes a two dimensional picture, if one embryo is behind the other, then it might be invisible on the sonogram.

This is much more likely in the first trimester, when the embryos are still small. After all, if there's less to hide, then it's easier for one to slip behind the other.

This happens a lot more often in mono-mono twins, which share the same amniotic sac and placenta (find out about the different types of twins here). Because they're so close together in the womb, it's much easier for one twin to slip behind the other and avoid prying eyes.

You might also ask yourself how a doctor can miss two separate heartbeats? Well, the first thing you have to realise is that in the case of twins, there would really be three heartbeats. Unless you've developed some magic zen buddhist technique to stop your heart as you have your scan. With so much noise, it can be difficult to differentiate between the heartbeats of you and your baby.

It's also possible that one or both heartbeats can be drowned out by your own, or beat almost perfectly in time with one another or yours, so they can't be heard separately.

So How Often Are Twins Missed on Ultrasound?

Not very often.

Like we said earlier, it's far more likely that one twin can be missed early in your pregnancy, and gets less and less likely, until it's almost impossible at about the 20th week.

Of course, all pregnancies are different, so never write anything off. I once heard a story of twins only being discovered as the mom to be was giving birth. Now there's a surprise you wouldn't forget!

So, to recap:

  • Twins can be missed on ultrasounds, but it's unlikely
  • It's more likely in the first weeks of pregnancy, and gets less likely as you go
  • Just because your scans miss twins isn't a reason to worry. No scan is completely foolproof

So even though it doesn't happen often, can an ultrasound miss twins?The answer is yes. Have you ever had this happen to you? Or maybe your ultrasound picked up twins really early, which was completely unexpected! Either way, we'd love to hear your story, so let us know in the comments! 

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