What is Nub Theory and Can It Be Trusted?

When you’re pregnant and the first thing that your friend and family always like to do is to predict whether you are going to have a baby boy or girl when the bump at your tummy is visually obvious at week 20. Some say that if you're carrying all out front or low, you will likely have a boy and if you're carrying all around and high, you will likely have a girl.

While it was fun to playing this guessing game but some expert sonographers reckon that they can tell the baby gender as early as 12 weeks and this is called nub theory.

What Is Nub Theory And When Can It Be Tested?

The "nub theory" is the idea that you can discover the gender of your unborn child before this has actually been confirmed by a doctor. You would usually find out the sex of your baby during at 20 week scan but the nub theory claims that you can actually find out earlier, from your 12 week scan onwards.

This theory is also know by many as the "angle of the dangle" because that's basically how you can discover if your child is male or female. In early pregnancy, both male and female baby have a genital tubercle, which will later develop into either a penis or clitoris. By studying the angle of the genital tubercle is pointing at, you can predict the gender of the fetus.

How Reliable Is The Theory?

The nub theory does have scientific reasoning behind it and is therefore pretty reliable, depending on what stage in the pregnancy you decide to try it out.

IF your baby is laying in the right position on their 12-week scan photo, there is a very high chances that you will get a clear shot at the nub to help determine if your baby is a boy or girl.

However, if they are lying at an awkward angle, it can be a bit of a guessing game. Although there is no actual medical research that proves the nub theory to be 100% accurate, many mums-to-be actually swear by the method in terms of discovering the gender of the baby.

How Does The Nub Theory Work?

Now that you've heard the basics, let's get into how the nub theory actually works. The "nub" basically looks like a little button that sticks out the end of baby’s body on the scan. This is the genital tube that will eventually determine the sex of the child.

While a male and female genital tube can look very similar but to determine whether the fetus is a male or female is depending on the nub pointing angle.


Female genital tubercle


Male genital tubercle

Photo credit: Marjorie England

As you can see, a female and male genital tubercle can look very similar.

How To Analyze The Nub

The nub theory says that if this is pointing upwards at a 30-degree angle or more, it's a boy. If the nub is less than 30 degrees or pretty straight, then the baby is a girl.

So, if you are lucky enough to have a scan photo with a good shot of the "nub", you can make your own determination of the gender before you are even told.


The nub position is pointing straight out and under 30-degree. This ultrasound image suggested that this is likely a baby girl.


The nub is angling at more than 30 degrees in relation to the spine. This ultrasound image suggested that this is likely a baby boy.

Here is a video explaining how to analyze the nub...

How Accurate Is Nub Theory?

Analysis At Week 11: A Guessing Game (48% Accuracy)

The average time that people like to guess the gender by using the nub theory is between 10-15 weeks. That being said using the nub theory at 11 weeks is not very accurate and is very much a guessing game. The nub will be difficult to see at 11 weeks because it is not as developed as what it would be in just a week or two.

Analysis At Week 12: Quite Accurate (91% Accuracy)

Even though there is only a week difference, it is much more likely to guess the gender based on the nub theory at week 12. The genital tubercle is more developed at this point and it will be much clearer if it's pointing up (boy) or straight (girl.)

Analysis At Week 13: Almost A Lock! (94% Accuracy)

At 13 weeks and over, the nub theory is as close to 100% accurate as possible. At this stage your babies "nub" is well on it's way to becoming a penis or vagina, which makes it so much easier to determine.

Sharing Is Caring

Like what you read so far? How about help us to spread this AWESOME post to your friend and family? Your shout-out will help to motivate us to create more great posts for you and everyone else. Thanks for your support!

Check out this post for 'What Is Nub Theory And Can It Be Trusted?'

Click to Tweet

How Long Has The Nub Theory Been Around?

Many people think that the nub theory is a brand new thing that has only been discovered recently but it was actually first talked about by a doctor in 1989. As the years have gone on more information on the nub theory has become available, both through books and online like the 2006 study by Z. Efrat and the 2012 study by Lubusky.

Why Is Early Gender Determination Is Medically Important?

Knowing the gender of your baby means much more than knowing which clothes to buy for him/her, it's actually really important for your doctor to find out the sex of the fetus as soon as possible.

Researchers do not spend years of research on thousands of pregnancies just to quench our burning curiosity to know baby's gender at the earliest possible moment.

In fact, gender determination is important because there might be some sex-linked diseases that the mother/father are carriers of that can only be passed to male babies. This is really important because it could help to avoid further tests that are intrusive and could cause possible harm to the baby.

If the ultrasound identified it’s a female baby, then there is no further testing needed. However, if it’s a baby boy, further invasive test like Chorionic Villus Sampling (CVS) or Amniocentesis is needed to determine if the baby is healthy.

What's Mothers Opinion On Nub Theory?

If you want further proof that the nub theory is accurate, here are some quotes from REAL mothers who it has worked for.

"Mine was right..the tech at my ultrasound at 12 weeks showed us and explained that theory and guessed a girl, she was right."


"Mine was correct, ultrasound at 11 weeks and 3 days. I compared at the web site and said I bet its a girl by the angle. Even though I was sure I would have another boy. But sure enough its a girl."

United Kingdom

"The nub theory was right for all three of my kids but don't take it as the gospel because it isn't 100%"

United Kingdom

Click Here to Leave a Comment Below 1 comments