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The Nub Theory - ARTICLE

What is the Nub Theory? 


One of the first things that goes through our minds when we receive our BFP is "who will you be?". We are so eager to start planning the future/for the arrival of our sweet little one, that we instantly run to the internet searching for answers. Are you craving sweets? Baby must be a girl! Are you carrying high? Boy! While these old wives tales are fun to try, they aren't very accurate for predicting the sex of your baby. So what is? 


What if we told you that you could find out the sex of your baby earlier than expected? How about as early as 12 weeks? Intrigued? All this is possible with the Nub Theory. Don't let the word theory fool you, it's anything but that. It is backed by science and can be up to 99% accurate. 


Don't believe us? Let us explain further.



Nub Theory- EXPLAINED 


The Nub Theory is a prediction method that uses your baby's own developing genitalia to predict his or her sex. 


From about 7 or 8 weeks in gestation fetuses will begin developing what is called a "Nub" or as it is referred to in scientific terms, a "Genital Tubercle". However this nub is still very much ambiguous in appearance, so boys and girls look identical. All nubs start off flat and parallel to the dorsal surface, meaning it will run parallel along with baby's spine. 


It's not until 12 weeks that the Nub truly begins to take shape. This is where the fun begins! Your baby's Nub will now begin going through rapid developmental changes that will allow us to better differentiate him or her from male or female. 


In baby boys, the Nub will begin to rise, and show an angle, while baby girls remain parallel. 

Nub Theory- Angle or No Angle? 


The nub can be viewed via ultrasound in a mid sagittal plane. As seen on Figure 1, if the nub is pointing at a caudal angel (downward towards the rump) and less than 30 degrees between the axis of the dorsal surface, that indicates female. If the nub is at a cranial angle (upwards towards the cranium) and at and angle greater than 30 degrees between the axis of the dorsal surface, this indicates male. 


This is referred to as "the angle of the dangle". 


The angle can be easy to identify, but can also be so slight, that you may miss it or mistake it for that of a girl angle. This is because not all babies develop at the same rate (Figure 2). 



(Figure 1)

early gender prediction

(Figure 2)








What makes the Nub Theory different from the rest of the prediction methods out there? We are glad you asked! 


Its simple really, this one is backed by science! 


Scientists have been studying fetal development for years and years, so it should come to no surprise that within their studies, is the development of fetal reproductive organs. Scientists can confirm that the Nub Theory CAN and has been proven to be up to 99% accurate...i mean, we are literally using their own genitalia to predict who they'll be. 


All nubs will at some point have a fork like appearance; in fact they all start off that way. Let's dig a bit deeper into what a nub truly is.. 


This forked nub is split into two parts. For girls, the bottom half, also known as the urogenital folds will develop into the labia minora, and the top half known as the genital tubercle will develop into the clitoris. For the male fetus, the genital tubercle will develop into the glans of the penis, the urogenital fold becomes the shaft and the labioscrotal fold matures into the scrotum.

the nub techs Uk
ultrasound scan
what is the nub theory

(Figure 3)



As the Nub Theory increases in popularity, you will have heard the good, the bad, and the ugly. Truth is, the Nub Theory isn't always guaranteed to work, especially if you don't know what to look for. 


When properly trained, the chances of a wrong prediction drops significantly. There are things to take into account while predicting using this method. 


• Clarity- The clarity of the scans you were provided with. If your scan is grainy, chances are that the accuracy of your prediction will drop. We need a clear photo of baby for best accuracy. 


• Nub -If your baby's Nub is not imaging fully. This could mean only half a nub is present, or perhaps baby's leg or cord is captured along with nub, making it hard to decipher what is what. 


• Gestational age- The main reason your prediction could fail, no matter how clear your scan is, is the gestational age of your baby at the time your scan was performed. This will have a huge impact on the accurate rate you are given. 


Figure 4 shows the impact the gestational age of baby can have on a Nub Theory prediction. This is because from 11 weeks till about 12.5, the Nub is still developing. A day can truly make all the difference. 

nub theory accuracy

(Figure 4)

Nub Theory- Worth It? 


Absolutely. We believe the future is Nub! In our experience, the Nub Theory IS more accurate than the conventional potty shot. There is no need to guess if you saw 3 lines or a penis on your scan anymore, with a sagittal view of baby, it is undeniably clear. View Figure 5 and see just how clear the sex of baby can be seen!

 (Figure 5)


So why are we stuck in our old ways?

Go on, give it try! Become a believer and put it to the test!



If you'd like to try it but don't know how to read your scan, let us do the work for you! It is our passion to provide expecting families with expert evaluations of their scans. Knowing the sex of your baby is only a click away. Visit to obtain a prediction using the highly accurate and Scientifically Proven Nub Theory!

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