Hidden Twin Ultrasound at Six Weeks: Is It Possible?

A hidden twin ultrasound at 6 weeks looks like a scan of a singleton – that’s the problem! How common are hidden twins, and what clues can you look for?

It can be enough of a surprise to find out that you’re having one baby ‒ let alone two.

And although it’s sometimes clear from your first ultrasound scan that you’re having twins, you might not find out until further on in your pregnancy.

So how common is a hidden twin ultrasound at six weeks?

It’s rare, but it could happen.

Let’s take a closer look.

In this article: 📝

What is a hidden twin?

A hidden twin pregnancy is when you find out later in your pregnancy that you’re having more babies than you originally thought.

The classic urban legend is turning up at the hospital in labor, delivering one baby, and then finding out that those “afterpains” are actually contractions bringing your new baby’s sibling into the world.

Let’s clear one thing up right at the top: with modern ultrasounds, surprise second newborns are almost unheard of.

Can a twin be missed at 6 week ultrasound?

Yes, hidden twins at 6 weeks is possible, but not all that common nowadays.

They used to be more of a thing, when doctors only had wooden Pinard stethoscopes to listen to the heartbeat (or heartbeats).

Think Call the Midwife, all you period drama fans.

But once you reach the middle of the second trimester, there really isn’t anywhere for a second baby to hide.

Your uterus is amazing, but it’s not that roomy.

Having said all this, ultrasounds can still miss things ‒ especially early in pregnancy.

Maybe it looks like you’re having a girl, but it’s actually a boy.

Maybe the measurements on the ultrasound tell you that you’re having a 10lb baby, but they arrive at a perfectly average 7lb 6oz.

Basically, at six weeks, when your little one is still only the size of a lentil, mistakes are easy to make.

How common is it to miss a twin at 6 week ultrasound?

Not all that common now ‒ it’s actually pretty rare.

Thanks to technological advances and more detailed ultrasound imagery, missing hidden twins at 6 weeks doesn’t happen often.

But it is possible ‒ all it takes is for one embryo to be in front of the other for the ultrasound, but they have to be pretty perfectly in place for your ultrasound technician to miss them.

Can a twin be missed at a six-week ultrasound?

If you’re having a six-week ultrasound, it’s usually because you’ve had fertility treatment, bleeding or cramping, or complications during a previous pregnancy.

The focus of early ultrasounds is usually on:

Measuring the size of the “yolk sac” where your little one is growing

Your body is still busy making the placenta that will support your baby until they’re born.

Until then, they’ve got this fancy sac.

Early measurement of it gives you a more accurate due date than just looking at the date your last period started.

Checking if the baby is growing in the uterus and not in your ovary or fallopian tube.

This is known as an ectopic pregnancy and can be very dangerous.

Your baby is so small at this point that the ultrasound is usually transvaginal (using an internal ultrasound wand inside your vagina).

At this stage, it lets your doctors see more clearly than the classic jelly on the belly ultrasound you’ll have later.

But even with this method, if you search for missed twin ultrasound pictures, you won’t see much more than a round shadow on the ultrasound.

Is 6 weeks too early to see twins on ultrasound?

Sometimes, yes, a 6-week ultrasound is too early to see twins.

Here’s why:

• They’re mono-mono twins that split from one egg and share an amniotic sac, so they look like one shadow on the ultrasound.
  
• They’re growing close together so one baby can hide behind the other.
  
• Their heartbeats which can’t always be heard at 6 weeks) are synced up, so they register on the scan as one heartbeat.

When do you find out you’re having twins?

So when do twins show up on ultrasound?

Well, if your early pregnancy is gloriously uneventful, most mamas-to-be find out that they’re having twins during an ultrasound at the end of the first trimester.

(This usually happens between 12 and 16 weeks, depending on where you live.)

At this point, your little one looks much more like a tiny human, and they’re much more likely to move when the ultrasound wand pokes them

Surprise! I’m not alone in here.

And when you get to the halfway mark, you’ll have your 20-week anatomy scan.

Here, your ultrasound tech will take a long, detailed look at your little one’s skeleton, brain, and heart.

They might get you to change position to coax your baby to lie the right way to have their measurements taken.

You might even be encouraged to try to wake your little peanut up by drinking something sweet before the scan.

So even if your twin has stayed hidden until the halfway point, there’s no hiding from this one.

Can an embryo split after 6 weeks?

What about having twins happen after your first-trimester scan?

It’s very unlikely, as most twin embryos split within the first 2 weeks of fertilization.

So, more often than not, if you don’t have twins in your first-trimester ultrasound, chances are you’ve got a single baby growing in there.

Hidden twin pregnancy symptoms

Mamas of twins will tell you that two babies somehow make more than twice the work.

Sometimes, this trend starts with your pregnancy symptoms.

Often, the first clue that you’re having two babies is that all of your symptoms are worse:

You’re more likely to have severe pregnancy nausea.

Hyperemesis Gravidarum, the kind of pregnancy nausea that often leaves mamas-to-be needing treatment for dehydration, is more common in twin pregnancies.

Fatigue is more likely to set in early.

Can’t keep your eyes open?

Could be because your body is working even harder to make two babies.

Mamas-to-be generally gain more weight if they’re carrying twins.

But if this is your first pregnancy and you have nothing to compare your symptoms to, it can be hard to tell.

And if you’ve been pregnant before and have a toddler running around​​, you’ve got an extra excuse for feeling more tired.

There are also some signs of a hidden twin pregnancy that are harder to second-guess.

Twin pregnancies tend to give you a higher hCG count

This is the hormone that pregnancy tests pick up in your urine.

So if you have a dark line on a test before your period is due or a high hCG reading on a blood test, it could be twins.

Your fundal height will be bigger

Later on, you might get another clue when your healthcare providers start to measure your fundal height (the distance between your pubic bone and the top of your bump).

Yep, it’s going to be larger if you have twins.

And sometimes women have a strong gut feeling or dream they’re having twins.

And who are we to rule that out?

However you find out that you’re having multiple babies, you can connect with other twin mamas in the Peanut Community.

Exciting times ahead!