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The Nub Theory Explained

What is The Nub Theory?

The nub theory is a fascinating and intriguing concept that explores the early development of genitalia during foetal growth. A nub is the baby's unformed reproductive organs, which eventually transform into either the clitoris and labia or the penis and scrotum.


The theory revolves around the angle of 'the nub' (alongside other factors to be explored later). The orientation of this nub can provide insights into whether you're expecting a boy or a girl.


By assessing the angle of the nub in comparison to the baby’s spine, the baby’s sex can be identified. Often referred to as the "angle of the dangle," it's widely accepted that if the nub is positioned at an angle below thirty degrees, the baby is likely female, and above thirty degrees, the baby is likely male.


When using the nub theory, it's also important to consider other anatomical elements. These include the position of the bladder as well as the length and shape of the nub itself.


For boys, look for a nub angled 30 degrees or more from the spine, often with a telltale "stacking" appearance. Stacking appears as a white blob or a shadow perched above a defining white line, symbolising the early formation of the penis with the developing scrotum nestled underneath.

Male Nubs


Male nub. (Confirmed by The Nubologists.)

In some cases, male nubs may not exhibit any stacking, often due to the baby's position not being captured optimally in the ultrasound image. In such scenarios, a short, bright white line is typically visible, with the bladder located just beneath it. There are other occasions where the nub is observed to have an upward tilt, rising away from the baby's rump. This results in a noticeable gap beneath it.


A rising male nub shot. (Both confirmed by The Nubologists.)

See below for a clear male nub shot, the most common for predicting a baby boy.


Developing penis and scrotum can be seen clearly with this nub shot. (Confirmed by The Nubologists.)

Female Nubs


A female nub. (Confirmed by The Nubologists.

For girls, the nub is typically flatter and smoother, measuring in less than 30 degrees relative to the spine. The nub might appear to dangle from the end of the baby's rump, pointing downwards, or in some cases, it projects outward in a manner playfully termed as a 'rocket nub.' It is also common to observe forked-shaped nubs in female foetuses, but it's important to note that this forked shape can appear in both sexes.


A female nub. (Confirmed by The Nubologists.) 

A female nub hanging off the rump of baby. (Confirmed by The Nubologists.) 


The Nub Theory is not reliable before the 12-week gestational period. Prior to this stage, all foetal nubs look alike, characterised by their elongated, smooth, and cylindrical shape. It is only after reaching 12 weeks that the foetal genitalia start to develop unique characteristics, making it feasible to accurately determine the baby's sex.

Picture credit: Majorie England       

science nub.jpeg

Picture credit: Science Source

During week 14 the external genitalia is fully formed and recognisable in both side profile and potty shot view. Ultrasound scans conducted closely to week 14 yield the highest accuracy. Nevertheless, scans done after 12 weeks and 5 days also offer a significantly high degree of precision in determining the baby's sex.

When can't the nub theory be used?


Imagine being able to peek into the future of your unborn baby, uncovering the mysteries of their sex way before the traditional gender reveal! The intriguing nub theory has enabled us to have an insight into the sex of your baby in the early stages of development. Similar to the status of evolutionary theory, the nub theory stands on firm scientific grounds. A nub, the early form of the genitals, encompasses both the labioscrotal fold and the dense nerve clusters that evolve into either the clitoris or the penis head.


Inaccurate predictions are usually attributed to poor-quality images, a limited number of images, or scans taken too early in the gestation period. In fact, inaccuracies due to the nub itself occur only about 5% of the time. 


When a video is available from around 12 weeks and 4 or 5 days of gestation, the accuracy of the nub theory in determining the sex is almost indisputable.

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