Hidden Twins: How It’s Possible for a Twin To Be Missed

I’m certain that many of us have been told a tale from an acquaintance that sounds like this:

“I know someone who had no idea she was carrying twins until her delivery!”

My mind always wonders how this is possible. With today’s technology, how on earth does a woman not know she is carrying twins?! 

Then I learned about hidden twins. I began to wonder:

The occurrence of a hidden twin is extremely rare, affecting 1-2% of all pregnancies. The timing of ultrasounds, the position of the twins, the angle of the ultrasound probe, and the skill of the technician performing the scan can all contribute to a hidden twin going unnoticed.

Let’s take a deeper look at the phenomenon of hidden twins and learn how they happen and what it means for a pregnancy. 

Understanding Hidden Twins

How can a twin be hidden? How exactly does that happen? Let’s find out. 

What Is a Hidden Twin?

A hidden twin refers to a situation where a woman is pregnant with multiple babies, but one (or more!) of the babies is not detected during routine ultrasound examinations. 

Can a Baby Be Missed on an Ultrasound?

Yes, it is possible for a baby to be missed on an ultrasound. Early in pregnancy, when the embryos are still small and developing, they may be difficult to visualize on an ultrasound scan.

Other factors, including the position of the twins, the angle of the ultrasound probe, or the skill of the technician performing the scan can contribute to a hidden twin going unnoticed. 

How Is a Hidden Twin Possible?

There are a number of reasons why a hidden twin can occur. The position of the twins or the size and shape of the uterus can make it difficult to detect all babies during an ultrasound examination.

Furthermore, if the twins are identical, they may share a placenta, which can make it even more difficult to distinguish between them on an ultrasound image. 

How Likely Is It To Have a Hidden Twin?

The likelihood of having a hidden twin varies depending on several factors, including the type of pregnancy (singleton, fraternal twins, or identical twins), the timing and quality of the ultrasound, and individual variations in fetal development.

Studies suggest that hidden twins occur in approximately 1%-2% of all pregnancies. 

Hidden Twin Pregnancy Symptoms

In some cases, there may be subtle clues or symptoms that hint at the presence of a hidden twin.

These can include unusually high levels of pregnancy hormones, excessive weight gain, rapid uterine growth, increased fetal movement, or inconsistent ultrasound findings. 

However, it’s important to keep in mind that these symptoms are not definitive proof of a hidden twin and can be present in singleton pregnancies as well. 

Hidden Twin vs. Vanishing Twin

It’s crucial to distinguish between a hidden twin and a vanishing twin.

A hidden twin refers to a situation where one or more babies are not detected during routine ultrasounds but continue to develop and are eventually born.

On the other hand, a vanishing twin occurs when two embryos are detected, but one of the embryos is then absorbed by the mother’s body, leaving one embryo in the womb. This can happen spontaneously. 

Detection and Diagnosis

So if hidden twins are a thing, how are they found?

How Are Hidden Twins Detected?

Hidden twins can be detected through regular ultrasound examinations during pregnancy. For example, perhaps a hidden twin was missed at one ultrasound but discovered at the next. 

The timing and frequency of ultrasounds play a significant role in the detection of hidden twins.

In early pregnancy, when the embryos are small and difficult to visualize, there is a higher chance of a hidden twin going undetected.

However, as the pregnancy progresses and the babies grow, they become more apparent on ultrasound scans. 

In some cases, hidden twins remain undetected for the duration of the pregnancy and aren’t discovered until birth! 

Hidden Identical Twin Ultrasound 5 Weeks

At 5 weeks gestation, the embryos are still in the early stages of development, and it can be challenging to visualize them on an ultrasound.

Identical twins may appear as a single gestational sac or as two sacs, depending on whether they share a placenta.

In some cases, the ultrasound may not reveal the presence of both embryos, leading to a hidden twin situation. 

Six-Week Ultrasound: Twins Missed

During the six-week ultrasound, the embryos are slightly larger and more defined. However, there is still a possibility of missing one of the twins due to their positioning, the angle of the ultrasound, or limitations in equipment.

It’s important to note that early ultrasounds have a higher chance of missing a hidden twin compared to later ultrasounds. 

Hidden Twin Ultrasound 8 Weeks

By 8 weeks, the embryos have grown larger, and their features are more distinguishable on ultrasound.

The chances of detecting a hidden twin increase at this stage, but there are still instances where one baby may remain hidden due to various factors. 

Hidden Twin Found at 20 Weeks

Around the 20-week mark, during the anatomy scan, hidden twins are often detected if they were missed in earlier ultrasounds.

By this stage, the babies have grown significantly, and their structures and movements are more prominent, making them easier to identify. 

35 Weeks Pregnant Hidden Twin

In rare cases, a hidden twin may go undetected until later in pregnancy, such as at 35 weeks.

There are stories, such as this one, where women do not discover they are carrying twins until much later on in their pregnancy. 

Surprise Twins at 37 Weeks

There have been instances where twins were not discovered until the mother went into labor or had a scheduled cesarean section at 37 weeks or later.

While these cases are rare, they highlight the potential for a hidden twin to remain undetected until the very end of pregnancy.

Can One Twin Hide Behind the Other Until Birth?

Yes, it is possible for one twin to hide behind the other until birth.

The positioning of the twins in the womb can sometimes result in one twin being fully or partially obscured by the other, making it difficult to detect during ultrasounds.

This situation, known as “hiding behind,” can lead to a surprising moment when the hidden twin is born. 

Risks and Impacts

Hidden twin pregnancies, just like normal twin pregnancies, are considered to be high risk and may require different levels of care, treatment, and preparation. 

Risks Associated With Twin Pregnancy

Twin pregnancies do carry higher risks compared to singleton pregnancies. These risks include preterm labor, low birth weight, gestational diabetes, preeclampsia, and complications during delivery.

It is crucial for women expecting twins, whether hidden or not, to receive regular prenatal care and closely monitor their health and the babies’ development. 

Preparing for a Surprise Set of Twins

Discovering a hidden twin can be a real shock for expectant parents, especially if the twin isn’t detected until delivery!

If you are lucky enough to discover a hidden twin before delivery, it is essential to make the necessary preparations for the arrival of two babies.

This includes updating the birth plan, arranging for additional support, having plenty of diapers on standby, and ensuring the practical aspects of childcare are in place. 

Twin Birth Plan

A birth plan is crucial for any pregnancy, but it becomes even more important in the case of twins.

While you can’t plan exactly how labor and delivery will go, you can have a tentative plan in place for a sense of security and comfort.

Discussing birthing options, such as vaginal birth or cesarean section, with healthcare providers is essential.

Understanding the potential challenges and being prepared for different scenarios can help parents navigate the birthing process more confidently and ensure the best possible outcome for both babies and the mother. 

Closing Thoughts

I think every parent is shocked when they discover they’re having twins. However, the shock factor probably doubles with a hidden twin!

Regardless, having twins (whether hidden or not) is a huge blessing and so much fun!