GTM-WG8XH27 google-site-verification: google95a6d318fda64b63.html The Nub Theory: How accurate is it? | Early Gender Prediction

The information provided to you is backed by many years of knowledge on the the theory. We are not medical professionals nor do we provide medical advice.

Because nothing is 100% but birth, we will no longer be offering refunds on incorrect gender predictions effective march 2020.

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Between 11 to 13 weeks in gestation, all babies have  a nub between their legs called the genital tubercle, and according to this theory the angle of the nub will indicate whether its a boy or a girl. If the nub is over 30 degrees up from the spine, its a boy - but if its under its a girl. All nubs will image as a fork. This fork is split into two parts.The bottom half also known as the urogenital folds will develop into the labia minora, and the top half will develop into the clitoris and will continue to retract into its final resting place in the weeks to come. The sex of your baby is chosen from the moment of conception. The nub can be viewed via ultrasound in a mid sagital plane. 


There is a lot of confusion around the bladder position and how this  helps determine your baby's gender. The bladder is not any different in males or females .

The bladder is used as an anchor to measure the axis to determine if this is above or below 30 degrees.


If you’re looking for more information regarding the nub theory, and keen to know your baby's gender as soon as possible, you’ve come to the right place. Here at The Nub Techs LTD, we will check the visibility of your baby's genital tubercle, the angle in which the nub points too, the shape and look of the overall nub, if stacking or shadowing is seen above the nub, and the bladder position in which we use as an anchor.

All factors mentioned above are taken into account when predicting your babys gender these factors are backed by science and with that proves to be a highly accurate way of determining gender as early as 12 weeks.

Before 10 weeks of pregnancy, the genital tubercle appears to be the same in both male and female fetus’s. Between 12-14 weeks there is a substantial difference in how the nub appears and so predicting at this gestation is up to 99.9% accurate. After 14 weeks, it is possible for the sonographer to determine gender at your appointment, however most ultrasound technicians will want to wait until at least 16 weeks when the genitals are easily viewed.


 A genital tubercle or phallic tubercle is a body of tissue present in the development of the reproductive system. It forms in the ventral, caudal region of mammalian embryos of both sexes, and eventually develops into a primordial phallus.

All babies have a ‘nub’ between their legs, this is called the genital tubercle, until about 7-8 weeks of pregnancy, both sexes will have a preliminary set of genitalia that will eventually differentiate to become either the male or female sex organs. This means, that both male and female genitalia start from the same foundation.  The genital tubercle comprises of three areas, the genital tuber, Urogenital fold and the labioscrotal fold.
​For male fetuses the genital tuber will develop into the glans of the penis,

the urogenital fold becomes the shaft and the labioscrotal fold matures into the scrotum.
​For female fetuses the urogenital folds develop into the Labia minora and the genital tuber continues development into the clitoris.



We get asked often, if a nub is showing as a fork it must be a girl? This information is actually incorrect. If the nub is angled greater than a 30 degree angle in relation to the spine and flicked up, it is likely you are having a baby boy. If it is pointing straight out, down, and under a 30 degrees angle, it is likely you are having a baby girl.

As you can see from our examples, we illustrate how a male fetus’ genital tubercle is angled above 30 degrees you can also see the tip of his nub point upwards indicating a baby boy. From the right we illustrate a female fetus' genital tubercle which is angled below 30 degrees, the nub points downwards and sits flush to her spine indicating a baby girl.

The length and shape of the genital tubercle may sometimes indicate gender, but not always. For example, some say that a “forked” shape at the tip is indicative of a girl fetus, however we do not adopt this, as its clear that both sexes can be seen with a forked nub in the early stages of development.  The reason you see a fork in the nub of both female and male fetuses, is because this fork serves an important purpose. For females, this fork will become the labia and clitoris, for males, the top half of the fork will develop into the penis, and bottom fork into the scrotum.We also know a forked nub is a sign of an undeveloped nub or a late riser (in males)


The "stacked" nub as it's most commonly known consist the developing penis and scotal line. Both can be seen imaging in bright white at the base of babys body. The penis is seen as a round shape, while scrotal line is located right underneath and longer in length imaging as a line.-- 

Female nubs can sometimes image in funny ways that make them appear as "stacked". This happens when the top part of the fork on baby's nub, also known as baby's clitoris has been captured at an off angle. These angles can often lead to much confusion and wrongful prediction of baby's sex in the nub theory community. 

(Predicting your babies gender from as early as 12 weeks)


In some of the study groups, when the angle of the genital tubercle was an intermediate angle of 10 to 30 degrees the fetal gender was not determined.Out of a total of 1619 pregnancies; gender was assigned and confirmed in 1424. The table below shows the results in so far for accuracy of fetal gender prediction at a routine first trimester scan. 

The fetal gender was assigned as male if the angle of the genital tubercle to a horizontal line through the lumbosacral skin surface (lower portion of the spine) was greater than 30 degrees and female when the genital tubercle was parallel or convergent (less than 10 degrees) to the horizontal line.


Prenatal gender assignment by ultrasound has a high accuracy rate at 12 to 14 weeks. At 11 weeks there was an error rate of 50% and only 14/100 assigned correct male gender. In the male fetuses after 12 weeks, there was a significant increase in the angle of the genital tubercle from the horizontal. The accuracy of sex determination increased with gestation.