top of page



nub theory explained

The Nub Theory Explained

The nub theory is the one and only theory you can count on. 

We see so many comments that this is "just a theory" and that it doesn't exist, even some sonographers will tell you they have never heard of it.

However, rest assured. We have studied this method for many years and we know that if your scan images are analysed correctly, using the many different gender markers, then the nub theory is up to 99.9% accurate. 


There are times when the nub theory will be incorrect, this is usually down to a poor image, the incorrect identification of all the gender markers and the wrong gestation submitted at the time of analysis. If a video is analysed by our team, then the theory is pretty inarguable. 

Usually if an incorrect prediction does happen it is generally due to the rise in nub or an inexperienced specialist. Thankfully our team here have the experience needed to predict with confidence.

So What Is A Nub?

A nub (phallic tubercle) is your baby's forming genitalia, the body of tissue present in the development of the reproductive system that will either form the urogenital fold (developing labia), or the labioscrotal (developing scrotum). Your baby's nub will always image as two lines,  the top half of this line in a girl nub will develop in to her clitoris and for a boy the top line of the nub will develop in to his penis.

 During the 12th week of pregnancy the nub is going through the rapid development changes and the accuracy of your prediction will be much higher. This will vary between 80-99% depending on the quality of the scan. Gestation plays a huge part, the exact gestation is a must, even one day wrong can make a huge difference in how the nub develops. For example, boy baby's at 12.6 weeks can image with a forked nub, this can be a telltale sign that his nub is undeveloped and in this case someone with an untrained eye in the theory will almost always predict a girl. We do not adopt this method, as there is always more to the nub than just the appearance.

Nub Theory For A Boy Nub

A boy nub in development varies at different gestation. The gender will usually be easier to predict if the nub is seen to be angled above 30 degrees or higher in relation to his spine. A boy nub doesn't always have to be seen as a typical boy shot and can appear forked, several gender markers will need to be taken in to account here to identify the forked nub as male. A lot of the time we do see these predicted as girl because of the fork shape, however the rise is what is most significant to determine the gender on these types of nubs. 

Example Of Boy Nub's 

Below you will see examples of risen boy nubs. The boy nubs here have angles greater than 30 degrees, using the bladder as an anchor to draw through, you will get a definite rise and the tip of the nub is also pointing up.


One of these nubs was predicted to be a girl elsewhere, he is now born.

the nub theory

Below is a clear penis and scrotum in development shot. The bright white density of the scrotum (bottom line) and the bright white density of the penis on the top. There are other gender markers we take into account here, the significant rise seen from the spine to the actual nub, the length of the nub and how the appearance of the stacking looks. This is the perfect boy nub and you can most definitely purchase blue.

stacked nub

Nub Theory For A Girl Nub

 Gestation plays a huge part and can be predicted incorrectly from the 12th week mark. This is due to the 15% chance of change, with the development still imminent, the baby can still rise and be confirmed a boy. However a lower gestation will be given for this reason and other possible markers seen to know if a rise could potentially happen on your baby.

Here we must look at the angle, a girl nub will image between a 10 and 29 degree angle.

Example Of Girl Nub's 

Clear parallel girl nubs. The girl nubs seen here are between 12-12.5 weeks in gestation and they have an angle of less than 30 degrees. The bladder is drawn through to the tip of the nub and shows no rise. The tip of the nub is also pointing down.

nub theory

The nub shot below shows developing clitoris and labia. With this kind of nub shot an accuracy of 99% can be given. This classic girl nub shows some clear gender markers. The nub will point down at the very tip towards the baby's rump and you will notice the nub hangs over the rump too.

A full long line (clitoris) will image and the bottom second line (labia) will show just at the tip. The nub looks forked but sits at an angle of less than 30 degrees. This is a sure sign to purchase pink. 

nub theory girl

A "stacked" girl nub, which many would predict boy on. This nub shows an angle less than 30 degrees, draws parallel and the tip is pointing downwards towards the rump.

the nub theory explained

Can We Predict At 11 Weeks?

Unfortunately we won't as we wouldn't want to get your hopes up for a specific gender. Some other sites will predict, its down to personal choice if you decide to go ahead, just always have in mind that the nub at 11 weeks looks pretty similar to a girl nub in its 12th week, so the prediction just isn't accurate enough. A nub is a small protrudent seen between the legs as early as 8 weeks. Both boys and girls start with a flat ambiguous nub, this is why most boys are inaccurately guessed as girls during the 11th gestational week. 

Example Of 11 Week Nub Shots

Here is a closer look at a girl and boy nub from 11 weeks, you can see below there's really not much difference in the appearance. These nub shots show a classic forked shape and they look very similar in appearance. One of these nubs was later confirmed boy and the other confirmed girl.

nub theory

Example Below  11-12 Weeks In Gestation The Difference In The Nub Appearance

As you can see in our examples below the 11.3 week nub shot shows a boyish appearance. This nub was predicted to be a boy through someone else. However the nub was still undeveloped and yet to go through the rapid changes, during the 12th week of development you can see the nub has now found its final resting place and at 12.2 weeks the nub now shows a clear girl shape. It's parallel to the baby's spine, angled at less than 30 degrees and the appearance is flush to baby's the rump. She was later confirmed girl.

nub theory 11 weeks
bottom of page