The Nub Theory

"I've waited 12 weeks already, how much more?"
- Very impatient mama who needs to know more!

What is the Nub theory?

The basics of the Nub theory are simple and straight forward (no pun intended), it's all about the angle of the genital tubercle. The confirmed boy nubs is usually angled upwards 30 degrees or more in relation to the spine, while nub theory girl says is either parallel or less than 30 degree from the spine. Several studies have been conducted and have found that, in controlled settings, nub theory ranges between 98% and 100% in accuracy. That is great odds for knowing your little one's gender before your doctor can confirm it!

For more information about what is the nub theory, here are a couple of the most recent studies conducted:
Ultrasound evaluation of fetal gender at 12–14 weeks
Fetal gender assignment by first‐trimester ultrasound

Want to read your Nub theory scan?

What is the nub on a baby scan? Both male and female start forming their genitalia in the very early weeks after conception, but it isn’t until 11-12 weeks that the differences can be seen. Although outward genitalia isn't fully formed until after 16 weeks, the angle of the genital tubercle can be seen from 11 to 15 weeks to determine gender. In the nub theory, there are two main struggles when trying to read your own ultrasound. Perhaps the trickiest part of reading your own ultrasound is being able to locate the nub. It is usually right under the legs, but because every image is different and babies like to move around during ultrasounds, it takes an expert eye to pinpoint it for sure. The second struggle is seeing more than just the basic angle, as at 11 and 12 weeks the boy nub might still be parallel, but with an expert eye the scrotum can began to be seen.

Nub Theory pictures

Nub theory examples

How read your own Nub theory ultrasound?

In order to be able to make a gender prediction the ultrasound in nub theory must display a profile view of the baby, and the nub must be visible, this can be a challenge because babies move and good profile views are hard to get. If you do achieve this image, here are the steps for nub method:

-Find the spine: The angle of the spine serves as a baseline to compare with the angle on the nub, which is our next step.

-Find the nub: It should be a defined white line along where the legs of the baby should be.

-Find the angle: Comparing the direction of the spine with nub, see if the angle is more or less than 30 degrees.

As mentioned above, in addition to the angle there are other factors that also need to be taken into consideration. Some believe that if a nub has some forking on the tip it is a male nub. Baby Gender Pros does not believe this to be true as we have seen make forked female nubs, however it is a marker that we look at closely. Shadowing above the nub or stacking are also markers that can be deciding factors towards our prediction.

Other gender prediction theories

Between 6 and 10 weeks

This baby gender prediction method uses the location of the placenta in early weeks of pregnancy to predict the gender of the baby. In controlled groups this method has been 97.5% accurate.


From 11 weeks

This early gender prediction theory uses skull marker to differentiate male and female babies. Although no studies have been conducted, this DIY gender prediction has been claimed to be up to 92% accurate.

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The Nub Theory
Average rating:  
 45 reviews
by Sarah on The Nub Theory
Got it right

Had the nub and skull test done, you guys predicted a girl but we are having a girl!

by Danielle W. on The Nub Theory
Thank you! You got it right!!!

After three sons, I found myself obsessed with what gender number four would be. You said girl based off of Ramzi, Skull, and nub theory. Finally Found out during ultrasound, and you were right! We’re so excited to meet our little girl. It was so fun to think about the possibility of you being right, and you were! Thank you! I would do this again!

by Bea Joseph on The Nub Theory
Its not right for me

You told based on the nub and the ramzi that its a girl I did the anatomy scan today its says boy,but it was fun thought knowing for 1 month that im having a girl😊

by Alexis on The Nub Theory
worth the money

I had my heart set on a boy, so when I got my prediction back I was excited. It really helped me bond with baby until our gender reveal! recommend

by Suzy on The Nub Theory
Nub and skull

You told me girl using nub and skull theory
I found out yesterday that it is a girl
Over the moon

by Heyly on The Nub Theory

I thought I could read the nub myself, boy was I wrong lol. Only ones that for my girl right.

by Leigh Ann on The Nub Theory
Baby Girl!

Cannons of pink smoke & confetti filled the sky on Saturday! Your prediction was accurate (14 weeks pregnant) We are having a girl! Yahoo!

by Joley on The Nub Theory
Boy nub theory

Nub theory said boy even though I couldn’t see anything lol but yup, it’s a boy

by Cindy on The Nub Theory

It’s a boy! Correct

by Mat on The Nub Theory

Having a princess and my wife was happy she used this. Real glad I gave it to her.

by Vanessa on The Nub Theory

Happy you were right

by Carla on The Nub Theory

For both my kids right so cheers to you

by Sofie on The Nub Theory
It’s a Boy

20 weeks and my doctor couldn't find out gender. I send you all my scans and you said boy and you were right. Today my doctor finally told my that it’s a boy.

by Lucy on The Nub Theory
Cross fingers

Had my gender scan and they said girl!!! You were right. Thanks

by Amy on The Nub Theory
It’s a boy

Update. you said boy with nub theory on my 12+4 scan. My little prince was born last month.

by Alen on The Nub Theory
Just Fun

results are not correct and its for fun only.

by Laura on The Nub Theory
Wrong result, but fun!

Your prediction was a girl.. I had a boy..but it was fun to get the results. Even my doctor got it wrong at 14 weeks.

by Kim on The Nub Theory
It’s a girl

It’s a Girl.!!! Omg your are right.🥰

by Hanna on The Nub Theory

Hi! Just wanted to let you know that my 20th week ultrasound said im expecting a boy, you were right!

by heather on The Nub Theory

Yes it's boy. you were correct

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